Transmission

ABSTRACT

A transmission includes a gear train, a transmission shaft driven by the gear train, a transmission casing incorporating the gear train and the transmission shaft, an axle driven by the gear train, a power take-off (PTO) unit attached to the transmission casing, and a parking brake. The transmission shaft and the axle are extended parallel to each other. The PTO unit includes a PTO input shaft, a PTO shaft, and a PTO drive train transmitting power from the PTO input shaft to the PTO shaft. The PTO input shaft is connected coaxially to the transmission shaft so as to receive power from the transmission shaft. The parking brake is provided on the transmission shaft or the PTO input shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 U.S.C. §119 to JapanesePatent Applications No. 2014-159397, filed on Aug. 5, 2014; No.2014-159398, filed on Aug. 5, 2014; and No. 2014-202081, filed on Sep.30, 2014, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a transmission, especially, a geartransmission.

Related Art

JP 2010-115969 A discloses a conventional four-wheel drive vehicle,e.g., a utility vehicle, including front and rear transaxles. The reartransaxle includes a transaxle casing incorporating a gear transmissionthat includes at least one gear train and a transmission output shaftdriven by the gear train. A power take-off (hereinafter, PTO) unitincludes a PTO input shaft, a PTO shaft, and a PTO gear train fortransmitting power from the PTO input shaft to the PTO shaft. The PTOunit is attached to the rear transaxle so as to drivingly connect thePTO input shaft coaxially to the transmission output shaft. The PTOshaft is drivingly connected to the front transaxle, so that the rotarypower of the transmission output shaft of the rear transaxle istransmitted to the front transaxle.

The vehicle includes a parking brake for braking axles drivinglyconnected to the gear train. The parking brake is disposed in a middleportion of the transaxle casing and on a transmission shaft of thetransmission at the upstream of the transmission output shaft connectedcoaxially to the PTO input shaft. The parking brake at this position maybe hidden by many surrounding parts. To access the parking brake,considerably many parts in the rear transaxle may have to bedisassembled. Therefore, this position of the parking brake isinconvenient for accessing the parking brake for maintenance or anotherpurpose.

JP S64-012856 A may be considered as teaching an arrangement of aparking brake in a transmission casing of a four-wheel drive vehicleadjacent to a sidewall of the transmission casing. This position of theparking brake is convenient for accessing the parking brake. However, inthe transmission casing, a transmission output shaft for driving rearaxles is extended in the fore-and-aft direction of the vehicle, theparking brake is disposed at one of right and left sides of thetransmission output shaft and includes a brake shaft extended parallelto the transmission output shaft, and a PTO shaft for driving frontaxles is disposed at the other of right and left sides of thetransmission output shaft and is extended parallel to the transmissionoutput shaft. A gear train is interposed between the transmission outputshaft and the parking brake, and other speed-change gear trains areinterposed between the transmission output shaft and the PTO shaft. Suchmany gear trains may reduce the brake force before it reaches the PTOshaft. If the vehicle is parked on a slope, the reduced braking forceonto the PTO shaft and the front axles may cause the vehicle tounexpectedly descend the slope.

JP 2006-292144 A discloses another conventional transaxle incorporatinga gear transmission. The gear transmission includes a transmission shafton which at least one gear for selecting a driving speed or direction isprovided rotatably relative to the transmission shaft. A gearshiftclutch is provided on the transmission shaft. The gearshift clutchincludes a clutch hub fixed on a transmission shaft, and a sleevespline-fitted on the clutch hub. The clutch hub and the gear are formedon outer peripheral portions thereof with respective splines. The sleeveis formed on an inner peripheral portion thereof with splines. Thesleeve is constantly spline-fitted to the clutch hub, and the sleeve isslidable in the axial direction of the clutch hub so as to be shiftablebetween a clutch-on position to engage its splines with the splines ofthe gear and a clutch-off position to disengage its splines from thesplines of the gear. The splines of the sleeve and the gear are formedwith chamfers for smoothening meshing of the splines.

Such a gearshift clutch is advantageously compact in comparison with asynchromesh system. However, the gearshift clutch still has a problem ofa slide lock of the sleeve such that the sleeve is hard to slide to meshits splines with the splines of the gear because tips of the splines ofthe sleeve formed with the chamfers abut against those of tips of thesplines of the gear formed with the chamfers. In this regard, the pitchof the splines of the clutch hub is the same as that of the splines ofthe gear, and the space between every adjoining splines of the clutchhub (and the gear) is substantially as wide in the peripheral directionof the transmission shaft as each spline of the sleeve, so that thesleeve cannot rotate relative to the clutch hub. If the difference inrotational position between the clutch hub and the gear causes that thesplines of the clutch hub and the splines of the gear are arranged quitealternately in the peripheral direction of the transmission shaft, thespaces among the splines of the gears are hidden behind the splines ofthe clutch hub from the splines of the sleeve, and each of the splinesof the gear blocks the spaces from each of the splines of the sleeve,thereby hindering the sleeve from further sliding toward the gear. Thisstate is defined as the slide lock of the sleeve. The slide lock is keptbefore the difference in rotational position between the clutch hub andthe gear is reduced to a level where the chamfers of the splines startto function properly.

The slide lock of the sleeve may often occur when a vehicle having beenstationary with an engine stopped is started by starting the engine. Anoperator may have to repeat a shift operation of a manipulator forsliding the sleeve between the clutch-off position and the clutch-onposition until the gear comes to an appropriate rotational positionrelative to the sleeve.

It is conceivable that the axial thrusting force for sliding the sleevein the direction to the gear should be increased to force the slide ofthe sleeve against the gear. However, such an increased axial thrustforce may shorten the life of component members of the gear clutch.Further, the increased force may increase a resistance of the gear whenthe meshing of the splines of the sleeve with the splines of the gear iscompleted as well as the resistance of the gear when the slide lock ofthe sleeve occurs, whereby the operator may feel the double resistancesduring the clutch-on operation of the sleeve to engage with the gear.

Moreover, JP 2004-08926 A discloses another conventional four-wheeldrive vehicle, e.g., a utility vehicle, provided with a parking brake.This parking brake is disposed in a rear transaxle drivingly connectedto a power unit including an engine and a transmission. This parkingbrake is a multi-friction disc type brake, which needs a large space forsufficiently lubricating the friction discs. A pawl engaging type brakemay be considered as an alternative parking brake adaptable to thevehicle because it is needs no lubrication fluid supply and is compact,however, such a brake having pawls needs a cam which may have to bedisposed stably in the vehicle so as to complicate design of thevehicle.

SUMMARY OF THE INVENTION

An object of the invention is to provide a transmission for a four-wheeldrive vehicle, wherein a parking brake is disposed at an appropriateposition for convenience of accessing the parking brake for maintenanceor another purpose, while the braking force of the parking brake can beefficiently and surely transmitted to all the wheels when the vehicletravels by driving four wheels.

To achieve the first object, a transmission according to the inventionincludes a gear train, a transmission shaft driven by the gear train, atransmission casing, an axle driven by the gear train, a PTO unit, and aparking brake. The transmission casing incorporates the gear train andthe transmission shaft. The PTO unit is attached to the transmissioncasing. The PTO unit includes a PTO input shaft, a PTO shaft, and a PTOdrive train transmitting power from the PTO input shaft to the PTOshaft. The transmission shaft and the axle are extended parallel to eachother. The PTO input shaft is connected coaxially to the transmissionshaft so as to receive power from the transmission shaft. The parkingbrake is provided on the transmission shaft or the PTO input shaft.

Therefore, the parking brake is located so that it can be easilyaccessed to enhance the efficiency of its maintenance. The parking brakeis interlocked directly (not via other gear trains) to the PTO drivetrain and the PTO shaft, thereby efficiently and surely transmitting itsbraking force to drive wheels (e.g., front wheels) drivingly connectedto the PTO shaft, whereby a vehicle parked on a slope, while being setin the four-wheel drive mode, is prevented from unexpectedly descendingthe slope. Further, the parking brake can be disposed in thetransmission casing or in a space surrounding the PTO input shaft,thereby needing no additional space for the parking brake.

Preferably, the transmission includes a bearing disposed in thetransmission casing to journal the transmission shaft. An end of thetransmission shaft projects outward from the bearing to be connected toan end of the PTO input shaft. The parking brake is provided on the PTOinput shaft.

Therefore, while the transmission output shaft is left in thetransmission casing, the PTO unit with the PTO shaft having the parkingbrake thereon can be attached or detached to and from the transmission.Further, the PTO unit can be easily exchanged for another PTO unitwithout a parking brake. Such a type variation of the PTO unit mayenhance a design variation of a vehicle equipped with the transmission.

Preferably, the PTO unit includes a PTO unit casing incorporating thePTO input shaft, the PTO shaft, and the PTO drive train. The PTO unitcasing is joined to the transmission casing so as to drivingly connect afirst end of the PTO input shaft coaxially to an end of the transmissionshaft. A second end of the PTO input shaft projects outward from the PTOunit casing so as to be provided thereon with the parking brake.

Therefore, the parking brake outside of the PTO unit casing can beaccessed more easily for maintenance or other purposes.

Preferably, the parking brake includes a fixed first pawl member, asecond pawl member, a locking member, and a locking operation member.The second pawl member is movable between a braking position to engagewith the first pawl member and an unbraking position to disengage fromthe first pawl member, in axial opposite directions of the transmissionshaft or the PTO input shaft, and is unrotatable relative to thetransmission shaft or the PTO input shaft. One of the axial oppositedirections is defined as a braking direction to locate the second pawlmember at the braking position so as to brake the transmission outputshaft and the PTO input shaft. The other of the axial oppositedirections is defined as an unbraking direction to locate the secondpawl member at the unbraking position so as to unbrake the transmissionoutput shaft and the PTO input shaft. The second pawl member has asurface to which a thrusting force in the unbraking direction caused bya counterforce from the first pawl member is applied in a directionperpendicular to the surface when the second pawl member engages withthe first pawl member. The locking member is movable between abrake-locking position and a brake-unlocking position in oppositedirections perpendicular to the braking and unbraking directions of thesecond pawl member. The locking member has a first surface parallel tothe surface of the second pawl member, and a second surface extendedslantwise from the first surface in the unbraking direction. While thesecond pawl member engages with the first pawl member, by locating thelocking operation member at the locking position, the locking member islocated at the brake-locking position so that the first surface abutsagainst the surface of the second pawl member so as to receive thecounterforce from the first pawl member, thereby preventing the secondpawl member at the braking position from moving in the unbrakingdirection. By moving the locking operation member from the lockingposition to the unlocking position, the locking member receives thethrusting force at the first surface and then at the second surface soas to move from the brake-locking position to the brake-unlockingposition so as to allow the second pawl member to move the unbrakingdirection.

Therefore, even if the first and second pawls engage with each other ina high torque condition so as to contain a torque, the thrusting forcecaused by the counterforce from the first pawl member is applied to thesecond pawl member so as to lighten the unbraking operation for movingthe second pawl member in the unbraking direction to disengage from thefirst pawl member. Such a parking brake can be configured simply at lowcost, and compactly so as to enhance a layout variation of componentelements in a vehicle.

A second object of the invention is to provide a transmission equippedwith a gearshift clutch solving the problem of the slide lock of asleeve of the gearshift clutch.

To achieve the second object, a transmission according to the inventionincludes a rotary shaft, a clutch hub, a gear, and a sleeve. The clutchhub is fitted on the rotary shaft rotatably integrally with the rotaryshaft. The clutch hub is formed on an outer peripheral portion thereofwith first splines. The gear is fitted on the rotary shaft rotatablyrelative to the rotary shaft so that the gear and the clutch hub areadjacently aligned in the axial direction of the rotary shaft. The gearis formed on an outer peripheral portion thereof with second splinesthat continue to the respective first splines when a rotational angle ofthe gear coincides to a rotational angle of the clutch hub. The sleeveis provided on the clutch hub so as to have an inner peripheral portionfacing the outer peripheral portion of the clutch hub. The sleeve isformed on the inner peripheral portion thereof with third splines thatare aligned alternately with the first splines of the clutch hub in theperipheral direction of the rotary shaft, so that the sleeve is slidableon the clutch hub in the axial direction of the rotary shaft, and isrestricted in rotating relative to the clutch hub. According to slide ofthe sleeve toward the gear, the third splines come to be alignedalternately with the second splines in the peripheral direction of therotary shaft so that the sleeve engages with the gear so as to berestricted in rotating relative to the gear, thereby drivinglyconnecting the gear to the rotary shaft via the sleeve and the clutchhub. The clutch hub, the gear and the sleeve are configured so as toallow the sleeve to rotate relative to the clutch hub so that the thirdsplines diverts to slide against the respective second splines afteraxial ends of the third splines contact axial ends of the secondsplines.

Therefore, due to the configuration to divert the third splines to slideagainst the second splines, the sleeve can smoothly slide to engage itsthird splines with the second splines of the gear, so as to reduce therepeat of the clutch on and off operation until the sleeve escapes fromthe slide lock. The gearshift clutch does not need to have a greatthrusting force to slide the sleeve against the slide lock, therebyensuring endurance of its component elements and reducing the doubleresistances during the clutch-on operation for sliding the sleeve toengage the third splines with the second splines of the gear.

Preferably, the axial ends of at least either the second or thirdsplines are formed with chamfers. Each third spline has first and secondguide spaces on opposite sides thereof in the peripheral direction ofthe rotary shaft between the adjoining first splines. Each of the firstand second guide spaces has a width not less than a width of the thirdspline in the peripheral direction.

Therefore, due to the sufficient width of each of the first and secondguide spaces relative to the width of the third spline, the secondspline can easily enter each of the first and second guide spaces as thesleeve slides to engage with the gear. As a result, the third splinescan easily reach positions adjacent to the respective second splines soas to completely engage the sleeve with the gear, thereby needing noadditional large or complicated device for guiding the third splines tothe positions.

Further preferably, the transmission includes a spline location devicethat locates the third splines so that the widths of the first andsecond guide spaces are equal to each other.

Therefore, both the first and second guide spaces have theabove-mentioned advantageous widths for guiding the third splines, sothat the above-mentioned effect of guiding the third splines to thepositions among the second splines to engage the sleeve with the gearcan be obtained in whichever direction the rotational position of thesecond splines of the gear deviates from the rotational position of thefirst splines of the clutch hub. Further, due to the equaling of thewidths of the first and second guide spaces, the widths of the guidespaces can be minimized so as to minimize the reduction in number of thefirst, second and third splines, thereby ensuring the required strengthof these splines and ensuring the required quietness.

Preferably, the spline location device includes a recess, a pressuremember, a biasing device, an angled portion, and guide surfaces. Therecess is provided in the clutch hub and having an open end at the outerperipheral portion of the clutch hub. When viewed in the axial directionof the rotary shaft, one of the first splines of the clutch hub is lostso that the open end of the recess is disposed at a positioncorresponding to the lost first spline. The pressure member is providedin the recess and having an end projecting outward from the open end ofthe recess. The biasing device biases the pressure member in a radialdirection of the rotary shaft toward the inner peripheral portion of thesleeve. The angled portion is formed at the inner peripheral portion ofthe sleeve between predetermined two of the third splines so that, whenthe end of the pressure member is located at the angled portion, a spacebetween one of the predetermined third splines and the pressure membercorresponding to the first guide space and a space between the other ofthe predetermined third splines and the pressure member corresponding tothe second guide space have respective widths in the peripheraldirection of the rotary shaft equal to each other. The guide surfacesare formed at the inner peripheral portion of the sleeve between theangled portion and one of the predetermined third splines and betweenthe angled portion and the other of the predetermined third splines.When the end of the pressure member is pressed against one of the guidesurfaces, the biasing device biases the end of the pressure membertoward the angled portion.

Therefore, during rotation of the rotary shaft, the rotating rotaryshaft causes a centrifugal force that assists the biasing device to biasthe pressure member toward the angled portion so as to ensure the effectof diverting the third splines when the sleeve slides to engage thethird splines with the second splines of the gear.

Alternatively, preferably, the spline location device includes a recess,a pressure member, a biasing device, an angled portion, and guidesurfaces. The recess is provided in sleeve and having an open end at theinner peripheral portion of the sleeve. The pressure member is providedin the recess and having an end projecting outward from the open end ofthe recess. The biasing device biases the pressure member in a radialdirection of the rotary shaft toward the outer peripheral portion of theclutch hub. The angled portion is formed at the outer peripheral portionof the clutch hub between predetermined two of the first splines sothat, when the end of the pressure member is located at the angledportion, the first and second guide spaces on the opposite sides of eachof the third splines have respective widths equal to each other. Theguide surfaces are formed at the outer peripheral portion of the clutchhub between the angled portion and one of the predetermined firstsplines and between the angled portion and the other of thepredetermined first splines. When the end of the pressure member ispressed against one of the guide surfaces, the biasing device biases theend of the pressure member toward the angled portion.

Therefore, the recess, the pressure member, and the biasing device areconfigured in the sleeve that is more accessible than the clutch hub,thereby improving the maintenanceablility.

These and other objects, features and advantages of the invention willappear more fully from the following detailed description of theinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a four-wheel vehicle 1.

FIG. 2 is a schematic plan view of a principal portion of vehicle 1,showing a transaxle 3 provided with a PTO unit 50.

FIG. 3 is a side view of PTO unit 50 attached to transaxle 3.

FIG. 4 is a sectional bottom view of a principal portion of PTO unit 50showing a parking brake 60 and a drive mode selection clutch 70.

FIG. 5 is a sectional bottom view of a principal portion of parkingbrake 60 set in an unbraking state.

FIG. 6 is a sectional bottom view of the principal portion of parkingbrake 60 being shifted to a braking state.

FIG. 7 is a sectional bottom view of the principal portion of parkingbrake 60 set in the braking state.

FIG. 8 is a sectional bottom view of the principal portion of parkingbrake 60 being shifted to the unbraking state.

FIG. 9 is a sectional bottom view of the principal portion of parkingbrake 60 showing activation of a brake shifter 63 to a lock pin 65.

FIG. 10 is a schematic plan view of the principal portion of vehicle 1,showing transaxle 3 provided with an alternative PTO unit 50A.

FIG. 11 is a schematic plan view of the principal portion of vehicle 1,showing transaxle 3 provided with an alternative PTO unit 50B.

FIG. 12 is a sectional plan view of transaxle 3 provided with analternative PTO unit 50C.

FIG. 13 is a sectional plan view of a principal portion of a geartransmission 10 in transaxle 3 showing a speed shifter 21.

FIG. 14 is a cross sectional view of a transmission output shaft 20(20A)provided with speed shifter 21, taken along XIV-XIV line of FIG. 13.

FIG. 15 is a schematic plan view of meshing of a spline of speed shifter21 with a clutch guide system 90.

FIG. 16A is a schematic plan view of meshing of the spline of speedshifter 21 that does not be provided with clutch guide system 90.

FIG. 16B is a schematic plan view of meshing of the spline of speedshifter 21 that does not be provided with clutch guide system 90.

FIG. 17 is a sectional side view of PTO input shaft 25 provided withspeed shifter 21 and a sleeve location device 96A.

FIG. 18 is a sectional plan view of speed shifter 21 and a sleevelocation device 96B.

FIG. 19 is a sectional side view of PTO input shaft 25 provided withspeed shifter 21 and sleeve location device 96B.

FIG. 20 is a schematic plan view of a four-wheel drive vehicle 100.

FIG. 21 is a side view partly in section of a front transaxle 107 with aclutch unit 139 for vehicle 100.

FIG. 22A is a perspective view of a brake operation system 190.

FIG. 22B is a perspective view of a brake flange 149.

FIG. 23 is a bottom sectional view of a principal portion of clutch unit139 showing a parking brake 141 set in an unbraking state.

FIG. 24 is a bottom sectional view of the principal portion of clutchunit 139 showing parking brake 141 set in a braking state.

FIG. 25 is a bottom view of parking brake 141 set in the braking state.

FIG. 26 is a sectional rear view of an alternative clutch unit 239.

FIG. 27 is a cross sectional view of clutch unit 239 taken alongXXVII-XXVII line of FIG. 26.

FIG. 28 is a sectional rear view of an alternative clutch unit 339.

FIG. 29 is a cross sectional view of clutch unit 339 taken alongXXIX-XXIX line of FIG. 28.

DETAILED DESCRIPTION OF THE INVENTION

A transmission according to a first embodiment, and a four-wheel drivevehicle 1 equipped with the transmission according to the firstembodiment will be described with reference to FIGS. 1 to 11. In thisembodiment, directions and positions of component members and portionsare defined on an assumption that vehicle 1 faces forward in a directiondesignated by an arrow F in FIG. 1.

An entire structure of four-wheel driving vehicle 1 will be describedwith reference to FIGS. 1 and 2. Vehicle 1 includes a vehicle body frame(chassis) 1 a, which supports a front transaxle 2 at a front portionthereof, and a rear transaxle 3 at a rear portion thereof

Right and left front wheels 6 have respective axels 6 a as rotary axesthereof. Front transaxle 2 includes a front transaxle casing 4 thatincorporates a front differential unit 33, and journals right and leftdifferential output shafts 35 of front differential unit 33. Right andleft coaxial differential output shafts 35 are extended rightward andleftward from front transaxle casing 4, and are drivingly connected torespective axles 6 a of right and left front wheels 6 via respectivepropeller shafts 37 with universal joints 36 and 38 at opposite ends ofrespective propeller shafts 37. Right and left front wheels 6 aresteerable wheels such that axles 6 a are connected to each other via atie rod 39 that is operatively connected to a steering operation device,such as a steering wheel (not shown).

Right and left rear wheels 7 have respective axels 7 a as rotary axesthereof. Rear transaxle 3 includes a rear transaxle casing 5 having arear portion, which incorporates a rear differential unit 40 andjournals right and left coaxial differential output shafts 45 of reardifferential unit 40. Incidentally, rear differential unit 40 isprovided with a differential locking device 49 on one of differentialoutput shafts 45 in rear transaxle casing 5. Right and left differentialoutput shafts 45 are extended rightward and leftward from rear transaxlecasing 5, and are drivingly connected to respective axles 7 a of rightand left rear wheels 7 via respective propeller shafts 47 with universaljoints 46 and 48 at opposite ends of respective propeller shafts 47.

Vehicle body frame 1 a supports an engine 8 serving as a prime mover ata fore-and-aft intermediate portion thereof between front transaxle 2and rear transaxle 3. Engine 8 has an engine output shaft 8 a extendedlaterally (in this embodiment, leftward). A front portion of reartransaxle casing 5 of rear transaxle 3 incorporating a gear transmission10 is disposed rearward from engine 8. Gear transmission 10 includeslaterally extended transmission shafts, i.e., a transmission input shaft11 and a transmission output shaft 20 parallel to each other. Therefore,engine output shaft 8 a, transmission input shaft 11 and transmissionoutput shaft 20 are extended parallel to each other and parallel todifferential output shafts 45 and axles 7 a of rear wheels 7.

Transmission input shaft 11 of gear transmission 10 is extendedlaterally (in this embodiment, leftward) outward from rear transaxlecasing 5 and parallel to engine output shaft 8 a. A belt-typecontinuously variable transmission 9 (hereinafter, referred to as CVT 9)is disposed at one of right and left sides (in this embodiment, leftside) of engine 8 and the front portion of rear transaxle 3 so as todrivingly connect engine output shaft 8 a to transmission input shaft11. CVT 9 includes a drive pulley 9 a on engine output shaft 8 a, adriven pulley 9 b on transmission input shaft 11, and a belt 9 cinterposed between pulleys 9 a and 9 b. CVT 9 serves as a mainspeed-change transmission, while gear transmission 10 serves as a subspeed-change transmission at the downstream of the main speed-changetransmission. Therefore, power of engine 8 is transmitted to reardifferential unit 40 for driving rear wheels 7 via CVT 9 and geartransmission 10.

Rear transaxle 3 will be described with reference to FIG. 2 in view ofFIG. 12 illustrating an alternative embodiment of rear transaxle 3. Geartransmission 10 includes a high speed forward gear train 10 a, a lowspeed forward gear train 10 b, and a reverse gear train 10 c. Geartrains 10 a, 10 b and 10 c are interposed between transmission inputshaft 11 and transmission output shaft 20 (or 20A in the embodiment ofFIG. 12). More specifically, in this embodiment, drive gears 12, 14 and16 of respective gear trains 10 a, 10 b and 10 c are fixed (or formed)on transmission input shaft 11, driven gears 13 and 19 of respectivegear trains 10 a and 10 c are fitted on transmission output shaft 20 (or20A) rotatably relative to transmission output shaft 20 (or 20A), and adriven gear 15 of low speed forward gear train 10 b is fitted on drivengear 13 of high speed forward gear train 10 a rotatably relative todriven gear 13. An idle gear 18 on an idle shaft 17 meshes with driveand driven gears 16 and 19, so that gears 16, 18 and 19 constitutereverse gear train 10 c.

A gearshift clutch 21 is provided on transmission output shaft 20 (or20A) between driven gears 13 and 19 of gear trains 10 a and 10 c.Gearshift clutch 21 is configured so as to selectively engage with oneor none of driven gears 13, 15 and 19 of respective gear trains 10 a, 10b and 10 c. Detailed description of the configuration of gearshiftclutch 21 and the gearshift pattern by use of gearshift clutch 21 willbe discussed later with reference to FIGS. 12 to 19.

Alternatively, gearshift clutch 21 may be provided on transmission inputshaft 11, drive gears 12, 14 and 16 of gear trains 10 a, 10 b and 10 cmay be provided on transmission input shaft 11 rotatably relative totransmission input shaft 11, and driven gears 13, 15 and 19 of geartrains 10 a, 10 b and 10 c may be fixed on transmission output shaft 20(or 20A).

In rear transaxle casing 5, a diametrically small gear 22 is fixed (orformed) on transmission output shaft 20 (or 20A), and meshes with adiametrically large gear serving as a differential input gear 42 of reardifferential unit 40. Therefore, gears 22 and 42 constitute a reductiongear train 10 d that transmits the rotary power of transmission outputshaft 20 (or 20A) as the output power of gear transmission 10 todifferential unit 40 for driving rear wheels 7.

Rear differential unit 40 includes a differential casing 41,differential input gear 42, at least one differential pinion 43, andright and left differential side gears 44. Differential input gear 42 isfixed on an outer peripheral portion of differential casing 41.Differential casing 41 is fitted on right and left differential outputshafts 45 so as to allow each of differential output shafts 45 to rotaterelative to differential casing 41. Right and left differential sidegears 44 are fixed on respective proximal ends of differential outputshafts 45 in differential casing 41. In differential casing 41, at leastone differential pinion 43 is pivoted on a differential pinon shaft 43 a(see FIG. 12) between right and left differential side gears 44, andmeshes with right and left differential side gears 44. Therefore, rightand left differential output shafts 45 are enabled by differentialpinion 43 meshing with differential side gears 44 to differentiallyrotate while right and left differential output shafts 45 rotatefollowing differential casing 41.

Differential locking device 49 includes a shift sleeve 49 a and at leastone lock pin 49 b. A right or left (in this embodiment, right) endportion of differential casing 41 is formed as a boss 41 a, which isextended along corresponding (in this embodiment, right) differentialoutput shaft 45. Shift sleeve 49 a is fitted on boss 41 a slidably alongboss 41 a. Lock pin 49 b is fixed to shift sleeve 49 a, and is extendedto constantly enter the inner space of differential casing 41 so as tobe unrotatable relative to differential casing 41. Shift sleeve 49 a isformed with an annular groove to engage with a fork operativelyconnected to a differential locking manipulator, e.g., a pedal or alever, so that shift sleeve 49 a is shiftable between an unlockingposition and a locking position.

When shift sleeve 49 a is disposed at the unlocking position, lock pin49 b is disposed close to differential side gear 44 fixed ondifferential output shaft 45 having boss 41 a thereon, however, lock pin49 b disengages from this differential side gear 44, thereby allowingthe differential rotation of right and left differential output shafts45 relative to differential casing 41. When shift sleeve 49 a isdisposed at the locking position, lock pin 49 b is inserted intodifferential side gear 44 so as to lock this differential output shaft45 with differential casing 41, thereby locking the differentialrotation of right and left differential output shafts 45.

Referring to FIG. 1, rear transaxle 3 is provided with a PTO unit 50having a PTO shaft 26, so that PTO unit 50 takes off power fromtransmission output shaft 20 of gear transmission 10 to PTO shaft 26.PTO unit 50 will be described in detail later. PTO shaft 26 is drivinglyconnected to an input shaft 31 of front transaxle 2 via propeller shafts27 and 29. In this regard, propeller shaft 27 is coupled at a rear endthereof to a front end of PTO shaft 26 via a coupling 57 (see FIG. 3),e.g., a spline sleeve, so as to extend forward coaxially to PTO shaft26. When viewed in plan, PTO shaft 26 and propeller shaft 27 aredisposed laterally eccentrically (in this embodiment, rightward) invehicle 1, and are extended straight in the fore-and-aft direction ofvehicle 1 at the right side of engine 8 and rear transaxle 3 laterallyopposite CVT 9 at the left side of engine 8 and rear transaxle 3. Inputshaft 31 of front transaxle 2 is disposed at a substantially laterallycenter of vehicle 1, so that, when viewed in plan, propeller shaft 29 isextended slantwise to connect the laterally eccentric propeller shaft 27to the laterally central input shaft 31. Propeller shaft 29 is coupledat a rear end thereof to a front end of propeller shaft 27 via auniversal joint 28, and is coupled at a front end thereof to a rear endof input shaft 31 via a universal joint 30.

Input shaft 31 projects at the rear end thereof rearward from fronttransaxle casing 4, and is fixedly provided (or formed) on a front endthereof with a bevel pinion 32 in front transaxle casing 4. In fronttransaxle casing 4, front differential unit 33 is provided with a beveldifferential input gear 34 meshing with bevel pinion 32, so that frontdifferential unit 33 distributes the rotary power of bevel differentialinput gear 34 between right and left differential output shafts 35.Front differential unit 33 is a limited slip differential unit, whichlimits the differential rotatability of right and left differentialoutput shafts 35. Therefore, if one of right and left front wheels 6 isgoing to be stuck, this front wheel 6 receives a driving torque fromdifferential output shaft 35 drivingly connected to the other frontwheel 6, so that vehicle 1 can be kept from being stuck.

PTO unit 50 will now be described in detail with reference to FIGS. 1 to9, on the assumption that PTO unit 50 is disposed at the right side ofrear transaxle 3 while CVT 9 is disposed at the left side of reartransaxle 3. Referring to FIGS. 2, 3 and 4, PTO unit 50 includes a PTOunit casing 51. PTO unit casing 51 includes a clutch housing 52 and agear housing 53. Clutch housing 52 is fixed to a right side surface ofrear transaxle casing 5 so as to extend rightward from rear transmissioncasing 5. Gear housing 53 is fixed to a right end of clutch housing 52.In this regard, referring to FIGS. 3 and 4, clutch housing 52 is formedwith right and left flanges defining right and left open ends thereof.The left flange of clutch housing 52 is fastened to the right endportion of rear transaxle casing 5 by bolts 58, and the right flange ofclutch housing 52 is fastened to a left end portion of gear housing 53by bolts 59. In this regard, gear housing 53 is formed with a left endhole 53 c into which a right end portion of clutch housing 52 can easilyinserted so as to facilitate assembling of housing 52 and 53. Further,by loosening bolts 58, clutch housing 52 can easily be separated fromrear transaxle casing 5 so that entire PTO unit 50 can easily bedetached from rear transaxle 3. By loosening bolts 59, gear housing 53can easily be separated from clutch housing 52, so that PTO unit 50 caneasily be disassembled.

Referring to FIGS. 3 and 4, clutch housing 52 includes a lower mainhousing 52 a and an upper operation housing 52 b joined to each other. APTO input shaft 25, a parking brake 60 and a drive mode selection clutch70 are disposed in main housing 52 a. A brake operation mechanism 78 anda clutch operation mechanism 83 are disposed in operation housing 52 b.

PTO input shaft 25 is disposed coaxially to transmission output shaft 20so as to extend rightward from transmission output shaft 20. In thisregard, referring to FIG. 3, a right end portion of transmission outputshaft 20 is journalled by a bearing 72 in rear transaxle casing 5, andprojects rightward from rear transaxle casing 5 into a shaft connectionchamber 51 a formed in a left end portion of clutch housing 52 so as tobe coupled to a left end portion of PTO input shaft 25 via a coupling56, e.g., a spline sleeve, in shaft connection chamber 51 a.

The left end of PTO input shaft 25 can easily be attached or detached toand from coupling 56 (inserted or released into and from coupling 56, ifcoupling 56 is the spline sleeve) provided on the right end oftransmission output shaft 20 simultaneously to the above-mentionedattachment or detachment of the left flange of clutch housing 52 to andfrom rear transaxle casing 5, thereby facilitating the attachment anddetachment of PTO unit 50 having PTO input shaft 25 to and from reartransaxle 3 having transmission output shaft 20.

Referring to FIG. 4, PTO input shaft 25 includes a left clutch inputshaft 23 and a right clutch output shaft 24 disposed coaxially to eachother. The above-mentioned left end portion of PTO input shaft 25coupled to the right end portion of transmission output shaft 20 viacoupling 56 is a left end portion of clutch input shaft 23. Therefore,by attaching PTO unit 50 to rear transaxle 3, clutch input shaft 23 isdrivingly connected to transmission output shaft 20. Moreover, clutchinput shaft 23 may be rotatably integrated with transmission outputshaft 20.

On the other hand, referring to FIGS. 3 and 4, clutch output shaft 24 isformed (or fixedly provided) on a right end portion thereof with a bevelgear 54 in a gear chamber 51 e formed in gear housing 53. Referring toFIGS. 2 and 3, in gear chamber 51 e, a bevel gear 55 is formed (orfixed) on a rear end portion of PTO shaft 26, and meshes with bevel gear54. Therefore, bevel gears 54 and 55 constitute a PTO gear train 50 adrivingly connecting clutch output shaft 24 of PTO input shaft 25 to PTOshaft 26. Bevel gears 54 and 55 may have equal diameters so that PTOgear train 50 a serves as an even speed ratio gear train. Alternatively,bevel gears 54 and 55 may have different diameters so that PTO geartrain 50 a serves as a speed-reduction (see the alternative embodimentshown in FIG. 12) or speed-increase gear train.

Clutch input shaft 23 is formed on a right end portion thereof with aprojection 23 a. Clutch output shaft 24 is formed in a left end portionthereof with a recess 24 a. Projection 23 a is fitted into recess 24 aso as to join the right end portion of clutch input shaft 23 to the leftend portion of clutch output shaft 24. However, projection 23 a isrotatable in recess 24 a so that clutch output shaft 24 is allowed torotate relative to clutch input shaft 23 unless drive mode selectionclutch 70 is engaged.

Referring to FIG. 4, clutch input shaft 23 is journalled by clutchhousing 52 via a left bearing 73 and a right bearing 74. Clutch outputshaft 24 is journalled by clutch housing 52 via a left bearing 75 and aright bearing 76. Clutch housing 52 is formed therein with a brakechamber 51 b between bearings 73 and 74, and with a clutch chamber 51 dbetween bearings 74 and 75. Parking brake 60 is provided on upstreamshaft 23 in brake chamber 51 b. Drive mode selection clutch 70 isprovided on the right end portion of clutch input shaft 23 in clutchchamber 51 d. Foresaid shaft connection chamber 51 a is formed betweenthe left end of clutch housing 52 and bearing 73.

Referring to FIG. 4, drive mode selection clutch 70 will be described.In clutch chamber 51 d, the right end portion of clutch input shaft 23and the left end portion of clutch output shaft 24 have splined outerperipheral portions. Drive mode selection clutch 70 includes a clutchshift sleeve 71 constantly spline-fitted on the splined outer peripheralportion of the right end portion of clutch input shaft 23. Clutch shiftsleeve 71 is slidable along clutch input and output shafts 23 and 24 soas to be shiftable between a two wheel driving (2WD) mode position Pc1and a four wheel driving (4WD) mode position Pc2.

When clutch shift sleeve 71 is set at 2WD mode position Pc1, clutchshift sleeve 71 is not fitted on the splined outer peripheral portion ofthe left end portion of clutch output shaft 24, thereby isolating PTOgear train 50 a and PTO shaft 26 from the rotary power of transmissionoutput shaft 20 and clutch input shaft 23 of PTO input shaft 25, wherebyfront transaxle 2 carrying front wheels 6 is isolated from the drivingpower of gear transmission 10, i.e., vehicle 1 travels in 2WD mode. Whenclutch shift sleeve 71 is set at 4WD mode position Pc2, clutch shiftsleeve 71 is fitted on the splined outer peripheral portion of the leftend portion of clutch output shaft 24, thereby transmitting the rotarypower of transmission output shaft 20 and clutch input shaft 23 of PTOinput shaft 25 to PTO gear train 50 a and PTO shaft 26, whereby fronttransaxle 2 carrying front wheels 6 receives the driving power from geartransmission 10, i.e., vehicle 1 travels in 4WD mode.

Referring to FIG. 3, vehicle 1 is provided with a drive mode selectionlever 86 serving as a manipulator for shifting clutch shift sleeve 71. Avertical upper clutch operation shaft 84 is journalled by a right endportion of operation housing 52 b, and is operatively connected to drivemode selection lever 86 via a link 85. Link 85 may have anyconfiguration. For example, link 85 may be a mechanical link including awire or a rod, or may be an electric link including an electronicactuator, e.g., an electric motor, or a hydraulic cylinder controlled bya solenoid valve, which may be connected to a switch which responds tothe shift of parking brake lever 81, thereby lightening an operator'soperational force. In this regard, an arm may be fixed on a top portionof upper clutch operation shaft 84 projecting upward from operationhousing 52 b so as to be connected to link 85.

Referring to FIG. 4, an annular groove 71 a is formed on clutch shiftsleeve 71. Referring to FIG. 3, a vertical lower clutch operation shaft82 is disposed in clutch housing 52 so as to engage at a bottom endthereof into annular groove 71 a. Clutch operation mechanism 83 isdisposed in gear housing 52 so as to operatively connect upper clutchoperation shaft 84 to lower clutch operation shaft 82 so that, whenupper clutch operation shaft 84 is rotated centered on its own axis byoperating drive mode selection lever 86, lower clutch operation shaft 82revolves centered on upper clutch operation shaft 84, whereby therevolution of lower clutch slider operation shaft 82 causes clutch shiftsleeve 71 to slide along PTO input shaft 25.

Parking brake 60 will be described with reference to FIGS. 3 to 9. Inbrake chamber 51 b, an outer peripheral portion of clutch input shaft 23is splined. Parking brake 60 includes a brake flange 61, a brake shifter62, and a lock pin 65. Brake shifter 62 is disposed in a main portion ofbrake chamber 51 b. Brake shifter 62 includes an inner sleeve 63 and anouter sleeve 64. Inner sleeve 63 is splined-fitted on the splined outerperipheral portion of clutch input shaft 23 so as to be axially slidableand unrotatable relative to clutch input shaft 23. Outer sleeve 64 isfitted on inner sleeve 63 so as to be axially slidable relative to innersleeve 63.

In an axial end (in this embodiment, right end) portion of brake chamber51 b, ring-shaped brake flange 61, serving as a first pawl member, isdisposed around clutch input shaft 23 so as to allow clutch input shaft23 passed therethrough to rotate relative to brake flange 61. The axialend portion of brake chamber 51 b is formed with recesses 51 c, whichare expanded centrifugally from the inner peripheral surface of clutchhousing 52 defining the main portion of brake chamber 51 b. Brake flange61 is formed with centrifugally expanded engagement projections 61 acorresponding to respective recesses 51 c. Engagement projections 61 aare inserted into respective recesses 51 c. Engagement projections 61 aof brake flange 61 and recesses 51 c may be formed similar to engagementprojections 349 of a brake flange 329 and recesses 350 in alater-discussed alternative embodiment as shown in FIG. 28. In this way,brake flange 61 is hindered by clutch housing 52 from moving axiallyalong clutch input shaft 23 and in the peripheral direction of clutchinput shaft 23. In other words, brake flange 61 is fixed to clutch unitcasing 51.

Inner sleeve 63 spline-fitted on clutch input shaft 23 is formed with aflange at an axial right end thereof facing brake flange 61 so as toserve as a second pawl member. A vertical left end surface of the flangeof inner sleeve 63 is defined as a retaining surface 63 e which cancontact a later-discussed vertical right pressure surface 64 e of outersleeve 64. Further, inner sleeve 63 is formed with pawls 63 a extendedrightward from a right end surface of the flange having retainingsurface 63 e at its left end. Brake flange 61 is formed with pawls 61 bon an axial left end thereof facing brake shifter 64. By sliding innersleeve 63 rightward along clutch input shaft 23 to brake flange 61,pawls 63 a mesh with pawls 61 b so that inner sleeve 63 engages withbrake flange 61 so as to hinder clutch input shaft 23 from rotatingrelative to unit housing 51. Referring to FIGS. 7 and 8, the position ofinner sleeve 63, where pawls 63 a of inner sleeve 63 mesh with pawls 61b of brake flange 61, is also defined as a right limit position for theslide of inner sleeve 63 relative to clutch input shaft 23. Thisposition is referred to as a braking position of inner sleeve 63.

A sleeve-shaped lock portion 63 b of inner sleeve 63 spline-fitted onclutch input shaft 23 is extended leftward from pawls 63 a along clutchinput shaft 23. A retaining ring 67 is fixed on clutch input shaft 23close to bearing 73 defining the left end of brake chamber 51 b.Referring to FIGS. 5 and 6, a position of inner sleeve 63, where lockportion 63 b of inner sleeve 63 contacts retaining ring 67 at a left endthereof, is defined as a left limit position for the slide of innersleeve 63 relative to clutch input shaft 23. This position is referredto as an unbraking position of inner sleeve 63.

Clutch input shaft 23 is formed therein with a radial pin recess 23 bhaving an end surface 23 c. Lock pin 65, serving as a locking member, isfitted in radial recess 23 b slidably in the radial direction of clutchinput shaft 23. Lock pin 65 is formed with a sleeve portion 65 a havinga spring chamber 65 e therein, so that spring chamber 65d is open at anend of lock pin 65 facing end surface 23 c of pin recess 23 b. Lock pin65 is formed with a hemispheric head 65 b at an end of sleeve portion 65a opposite the open end of spring chamber 65 e. A spring 66 isinterposed between an end surface of spring chamber 65 e and end surface23 c of pin recess 23 b so as to constantly bias lock pin 65 in thedirection for making head 65 b of lock pin 65 project outward from pinrecess 23 b.

Lock portion 63 b of inner sleeve 63 is formed through a left portionthereof with a radial pin hole 63 c. When inner sleeve 63 is disposed atthe braking position, head 65 b of lock pin 65 biased by spring 66enters pin hole 63 c. When inner sleeve 63 is disposed at the unbrakingposition, pin hole 63 c is disposed leftward from radial recess 23 b ofclutch input shaft 23 so that the inner peripheral surface of lockportion 63 b of inner sleeve 63 contacts head 65 b of lock pin 65 so asto press lock pin 65 in recess 23 b against spring 66.

Lock portion 63 b is fixedly provided peripherally on a left end portionthereof with a retaining ring 68. Outer sleeve 64, serving as a lockingoperation member, is axially slidably fitted on an outer peripheralsurface of lock portion 63 b of inner sleeve 63. Referring to FIGS. 5and 7, a position of outer sleeve 64 contacting retaining ring 68 oninner sleeve 63 at a left portion thereof is defined as a left limitposition for the slide of outer sleeve 64 relative to inner sleeve 63.This position is referred to as an unlocking position of outer sleeve 64relative to inner sleeve 63. On the other hand, referring to FIGS. 6 and8, a position of outer sleeve 64 where contacting retaining surface 63 eof inner sleeve 63 at a right end thereof is defined as a right limitposition for the slide of outer sleeve 64 relative to inner sleeve 63.This position is referred to as a locking position of outer sleeve 64relative to inner sleeve 63.

More specifically, outer sleeve 64 is formed so that its right portionis diametrically smaller than its left portion. An inner peripheralsurface of the diametrically small right portion of outer sleeve 64 isdefined as a slidable fitting surface 64 b that axially slidablycontacts the outer peripheral surface of lock portion 63 b of innersleeve 63. An outer peripheral portion of the diametrically small rightportion of outer sleeve 64 is formed with an annular groove 64 a, intowhich a later-discussed lower brake operation shaft 77 is fitted. Aright end portion of outer sleeve 64 is defined as a right end ofannular groove 64 a, and its vertical right end surface is defined as apressure surface 64 e that can contact retaining surface 63 e of innersleeve 63. The above-mentioned locking position of outer sleeve 64relative to inner sleeve 63 means the position where pressure surface 64e of outer sleeve 64 contacts retaining surface 63 e of inner sleeve 63.

An inner peripheral surface of the diametrically large left end portionof outer sleeve 64 is defined as a retaining surface 64 d that is spacedfrom the outer peripheral surface of inner sleeve 63. Therefore, outersleeve 64 is formed with a tapered inner peripheral surface 64 cextended from a left end of slidable fitting surface 64 b to a right endof retaining surface 64 d. The above-mentioned unlocking position ofouter sleeve 64 relative to inner sleeve 63 means the position wheretapered inner peripheral surface 64 c of outer sleeve 64 contactsretaining ring 68 on inner sleeve 63.

Referring to FIG. 9, while inner sleeve 63 is disposed at the unbrakingposition where the left end of inner sleeve 63 contacts retaining ring67 as shown in FIGS. 5 and 6, head 65 b of lock pin 65 is kept at abrake-unlocking position L1, where head 65 b of lock pin 65 is pressedin pin recess 23 b. On the other hand, while inner sleeve 63 is disposedat the braking position where pawls 61 b and 63 a mesh with each other,head 65 b of lock pin 65 enters pin hole 63 c, and to how much degreehead 65 b of lock pin 65 projects outward from the outer peripheralsurface of clutch input shaft 23 depends on positions of inner and outersleeves 63 and 64. If outer sleeve 64 is disposed at the lockingposition relative to inner sleeve 63 as shown in FIG. 7, head 65 b oflock pin 65 greatly projects outward so as to reach a brake-lockingposition L3 where head 65 b abuts against retaining surface 64 d ofouter sleeve 64. If outer sleeve 64 is disposed at the unlockingposition relative to inner sleeve 63 as shown in FIG. 8, head 65 b oflock pin 65 projects a little outward so as to reach an inner-sleevelocking position L2 where head 65 b abuts against slidable fittingsurface 51 b of outer sleeve 64.

Referring to FIGS. 5 to 8, four shift positions are defined for theslide of outer sleeve 64 relative to clutch input shaft 23. An unbrakingposition Pb1, as shown in FIG. 5, is a leftmost shift position of outersleeve 64 relative to clutch input shaft 23, where tapered innerperipheral surface 64 c of outer sleeve 64 abuts against retaining ring68, and the left end of inner sleeve 63 abuts against retaining ring 67.In other words, outer sleeve 64 set at unbraking position Pb1 is locatedat the unlocking position relative to inner sleeve 63 located at theunbraking position.

A braking position Pb3, as shown in FIG. 7, is a rightmost shiftposition of outer sleeve 64 relative to clutch input shaft 23, wherepressure surface 64 e of outer sleeve 64 abuts against retaining surface63 e of inner sleeve 63, and pawls 61 b and 63 a mesh with each other.In other words, outer sleeve 64 set at braking position Pb3 is locatedat the locking position relative to inner sleeve 63 located at thebraking position.

There is a first intermediate shift position Pb2, as shown in FIG. 6, onthe way of the sliding of outer sleeve 64 from unbraking position Pb1 tobraking position Pb3. At first intermediate shift position Pb2, pressuresurface 64 e of outer sleeve 64 abuts against retaining surface 63 e ofinner sleeve 63, and the left end of inner sleeve 63 abuts againstretaining ring 67. In other words, outer sleeve 64 set at firstintermediate shift position Pb2 is located at the locking positionrelative to inner sleeve 63 located at the unbraking position.

There is a second intermediate shift position Pb4, as shown in FIG. 8,on the way of the sliding of outer sleeve 64 from braking position Pb3to unbraking position Pb1. At second intermediate shift position Pb4,tapered inner peripheral surface 64 c of outer sleeve 64 abuts againstretaining ring 68, and pawls 61 b and 63 a mesh with each other. Inother words, outer sleeve 64 set at second intermediate shift positionPb4 is located at the unlocking position relative to inner sleeve 63located at the braking position.

As discussed later, by shifting the position of outer sleeve 64 relativeto clutch input shaft 23, inner sleeve 63 is located at either theunbraking position as its left limit position, where inner sleeve 63contacts retaining ring 67, or the braking position as its right limitposition, where pawls 49 b and 50 a mesh with each other.

Referring to FIG. 3, vehicle 1 is provided with a parking brake lever 81serving as a manipulator for shifting outer sleeve 64 of brake shifter63. Parking brake lever 81 is rotatably shiftable between an unbrakingposition (not shown) for locating outer sleeve 64 at unbraking positionPb1 to disengage pawls 63 a of inner sleeve 63 from pawls 61 b of brakeflange 61 and a braking position (not shown) for locating outer sleeve64 at braking position Pb3 to engage pawls 63 a with pawls 61 b. Avertical upper brake operation shaft 79 is journalled by a laterallyintermediate portion of operation housing 52 b, and is operativelyconnected to parking brake lever 81 via a link 80. Link 80 may have anyconfiguration. For example, link 80 may be a mechanical link including awire or a rod, or may be an electric link including an electronicactuator, e.g., an electric motor, or a hydraulic cylinder controlled bya solenoid valve, which may be connected to a switch which responds tothe shift of parking brake lever 81, thereby lightening an operator'soperational force. In this regard, an arm may be fixed on a top portionof upper brake operation shaft 79 projecting upward from operationhousing 52 b so as to be connected to link 80.

Referring to FIG. 3, a vertical lower brake operation shaft 77 isdisposed in clutch housing 52 so as to engage at a bottom end thereofinto annular groove 64 a. Brake operation mechanism 78 is disposed ingear housing 52 so as to operatively connect upper brake operation shaft79 to lower brake operation shaft 77 so that, when upper brake operationshaft 79 is rotated centered on its own axis by operating parking brakelever 81, lower brake operation shaft 77 revolves centered on upperbrake operation shaft 79, whereby the revolution of lower clutch slideroperation shaft 77 causes outer sleeve 64 to slide relative to clutchinput shaft 23 of PTO input shaft 25.

A breaking operation of parking brake 60 will be described withreference to FIGS. 5 to 7 and 9. When parking brake lever 81 is set atthe unbraking position, outer sleeve 64 abuts at tapered innerperipheral surface 64 c against retaining ring 68, whereby outer sleeve64 is retained at unbraking position Pb1 as shown in FIG. 5. Thepressure of outer sleeve 64 against retaining ring 68 is appliedleftward onto inner sleeve 63, and inner sleeve 63 leftwardly pressed byouter sleeve 64 abuts against retaining ring 67, whereby inner sleeve 63is retained at its unbraking position, i.e., its left limit position. Inthis state, pawls 63 a of inner sleeve 63 are separated from pawls 61 bof brake flange 61, thereby keeping clutch input shaft 23 from beingbraked by brake flange 61. Therefore, if drive mode selection clutch 70is engaged to set vehicle 1 in the 4WD mode, the rotary power oftransmission output shaft 20 is transmitted to PTO shaft 26 for drivingfront wheels 6. Further, in this state, head 65 b of lock pin 65 isdisposed at brake-unlocking position L1 as shown in FIG. 9, so thatinner sleeve 63 is allowed to slide rightward to brake flange 61.

By shifting parking brake lever 81 to the braking position, outer sleeve64 starts to slide at slidable fitting surface 64 b thereof on innersleeve 63 rightward away from retaining ring 68. Inner sleeve 63 is keptat its unbraking position until rightward moving outer sleeve 64 reachesfirst intermediate shift position Pb2 as shown in FIG. 6. When outersleeve 64 reaches first intermediate shift position Pb2, pressuresurface 64 e comes to contact retaining surface 63 e of inner sleeve 63.Afterward, as outer sleeve 64 moves rightward, inner sleeve 63 is pushedat retaining surface 63 e by pressure surface 64 e of outer sleeve 64moving rightward, so that inner sleeve 63 moves rightward together withouter sleeve 64. Finally, outer sleeve 64 reaches braking position Pb3as shown in FIG. 7, so that inner sleeve 63 reaches its brakingposition, i.e., its right limit position, whereby pawls 63 a of innersleeve 63 come to mesh with pawls 61 b of brake flange 61, therebybraking clutch input shaft 23 of PTO input shaft 25. The braking forceapplied on clutch input shaft 23 by parking brake 60 is transmitted torear wheels 7 via transmission output shaft 20 and differential unit 40.If drive mode selection clutch 70 is engaged, the braking force appliedon clutch input shaft 23 is also transmitted to PTO shaft 26 for drivingfront wheels 6 via clutch output shaft 24 and PTO gear train 50 a.

Further, when outer sleeve 64 reaches breaking position Pb3, pin hole 63c of inner sleeve 63 coincides to pin recess 23 b of clutch input shaft23, and slidable fitting surface 64 b of outer sleeve 64 is disposedrightward from pin hole 63 c, so that lock pin 65 projects through pinhole 63 c and head 65 b of lock pin 65 reaches brake-locking position L3as shown in FIG. 9, where head 65 b contacts retaining inner peripheralsurface 64 d of outer sleeve 64. Therefore, lock pin 65 prevents bothinner and outer sleeves 63 and 64 from unexpectedly moving leftward,i.e., in an unbraking direction Dr as shown in FIGS. 5 to 8.

While head 65 b of lock pin 65 is kept at brake-locking position L3, aright portion of an inner peripheral surface 63 b 2 of inner sleeve 63defining pin hole 63 b is kept at a position Pal, where the rightportion of inner peripheral surface 63 b 2 defining pin hole 63 bsubstantially contacts a right outer peripheral surface of sleeveportion 65 a of lock pin 65. Pin hole 63 b has a constant diameter sothat inner peripheral surface 63 b 2 of inner sleeve 63 defining pinhole 63 b is parallel to the outer peripheral surface of sleeve portion65 a of lock pin 65, except that only an open end portion of innerperipheral surface 63 b 2 defining pin hole 63 b facing the outerperipheral surface of clutch input shaft 23 is tapered so as to be ableto abut against hemispheric head 65 b of lock pin 65 when head 65 b isdisposed at inner sleeve locking position L2 as discussed later.

In this regard, while pawls 63 a mesh with pawls 61 b, inner sleeve 63receives a counterforce T1 a from brake flange 61 so as to be thrustleftward in unbraking direction Dr. Due to this counterforce T1 a, innersleeve 63 has a leftward thrusting force T1 b. Therefore, the rightportion of inner peripheral surface 63 b 2 of inner sleeve 63 definingpin hole 63 b and the right portion of the outer peripheral surface ofsleeve portion 65 a of lock pin 65 are perpendicular to the direction ofthrusting force T1 b, so that thrusting force T1 b is fully appliedperpendicularly to the right portion of the outer peripheral surface ofsleeve portion 65 a without diverting, whereby lock pin 65 surely keepsinner sleeve 63 at the right limit position (braking position) fromunexpectedly moving in unbraking direction Dr.

An unbraking operation of parking brake 60 will be described withreference to FIGS. 7, 8 and 9. By shifting parking brake lever 81 havingbeen set at the braking position to the unbraking position, outer sleeve64 starts to slide leftward in unbraking direction Dr at slidablefitting surface 51 b thereof on inner sleeve 63 so as to separatepressure surface 64 e from retaining surface 63 e of inner sleeve 63having pawls 63 a meshing with pawls 61 b of brake flange 61. At thestart of sliding of outer sleeve 64 in unbraking direction Dr, retaininginner peripheral surface 64 d of outer sleeve 64 slides against head 65b of lock pin 65 so that head 65 b is held at brake-locking position L3until tapered inner peripheral surface 64 c of outer sleeve 64 abutsagainst head 65 b. In this regard, head 65 b of lock pin 65 is extendedslantwise in unbraking direction Dr from the right portion of the outerperipheral surface of sleeve portion 65 a which contacts the rightportion of inner peripheral surface 63 b 2 of inner sleeve 63 definingpin hole 63 b.

As outer sleeve 64 slides in unbraking direction Dr after tapered innerperipheral surface 64 c abuts against head 65 b, tapered innerperipheral surface 64 c moving in unbraking direction Dr depresses head65 b. Then, slidable fitting surface 64 b of outer sleeve 64 comes toabut against head 65 b so that head 65 b of lock pin 65 is disposed atinner sleeve locking position L2. Head 65 b is held at inner sleevelocking position L2 during the slide of outer sleeve 64 in unbrakingdirection Dr until outer sleeve 64 reaches second intermediate shiftposition Pb4, where tapered inner peripheral surface 64 c comes to abutagainst retaining ring 68. Therefore, once the slide of outer sleeve 64in unbraking position Dr (leftward) from second intermediate shiftposition Pb4 starts, for example, when outer sleeve 64 reaches aposition Pa2, the tapered portion of inner peripheral surface 63 b 2 ofinner sleeve 63 defining pin hole 63 c comes to abut againsthemispherical head 65 b of lock pin 65 disposed at inner sleeve lockingposition L2 so that inner sleeve 63 applies leftward thrusting force T1b on head 65 b. As inner sleeve 63 pushed by outer sleeve 64 viaretaining ring 68 slides in unbraking direction Dr, leftward thrustingforce T1 b of the tapered portion of inner peripheral surface 63 b 2 ofinner sleeve 63 abutting against head 65 b functions to depress head 65b. Finally, depressed head 65 b of lock pin 65 reaches brake-unlockingposition L1 so as to allow inner sleeve 63 to slide in unbrakingdirection Dr freely from lock pin 65. When outer sleeve 64 reachesunbraking position Pb1, inner sleeve 63 reaches its unbraking position(left limit position) were inner sleeve 63 abuts at the left end thereofagainst retaining ring 67, whereby pawls 63 a of inner sleeve 63disengage from pawls 61 b of brake flange 61.

Referring to FIG. 10, an alternative PTO unit 50A is similar to PTO unit50 except that parking brake 60 is not provided in PTO unit casing 51 ofPTO unit 50A incorporating drive mode selection clutch 70 but isprovided on transmission output shaft 20 in rear transaxle casing 5.Parking brake 60 is disposed on the end portion of transmission outputshaft 20 adjacent to the opening of rear transaxle casing 5 to which PTOunit casing 51 of PTO unit 50A is joined, thereby being easily beaccessed via the opening of rear transaxle casing 5 so as to facilitateits maintenance, although parking brake 50 remains in rear transaxlecasing 5 after PTO unit 50 is detached from rear transaxle 3.

Referring to FIG. 11, an alternative PTO unit 50B includes analternative PTO input shaft 25A (more specifically, a clutch outputshaft of PTO input shaft 25A, if it is divided into clutch input andoutput shafts), which is fixedly provided thereon with bevel gear 54,similar to PTO input shaft 25. However, PTO input shaft 25A is furtherextended rightward from bevel gear 54 and projects outward from analternative PTO unit casing 51A so as to have an alternative parkingbrake 60A on an outer end thereof. Parking brake 60A disposed at thisposition may be further easily accessed for its maintenance. Parkingbrake 60A is illustrated as a friction disc type brake including afriction disc 69 connected to the right end of PTO input shaft 25A and abrake shoe 69 a to nip an outer peripheral edge of friction disc 69.However, parking brake 60A may be configured in any way as far as it isdisposed at this position.

Incidentally, PTO unit casing 51A of PTO unit 50B is divided into afirst housing 52A and a second housing 53A. First housing 52A journalsPTO input shaft 25A, however, does not incorporate a drive modeselection clutch. Second housing 53A incorporates PTO gear train 50 aand drive mode selection clutch 70. In this regard, an alternative PTOshaft 26A journalled by second housing 53A is divided into a clutchinput shaft 26 a and clutch output shaft 26 b. Drive mode selectionclutch 70 is provided on PTO shaft 26A so that drive mode selectionclutch 70 selectively engages clutch output shaft 26 b to clutch inputshaft 26 a for setting the 4WD mode of vehicle 1 or disengages clutchoutput shaft 26 b from clutch input shaft 26 a for setting the 2WD modeof vehicle 1.

Referring to FIG. 12, rear transaxle 3 is provided with an alternativePTO unit 50C. PTO unit 50C includes a PTO unit casing 51B that isdetachably attached to rear transaxle casing 5. In this embodiment, geartransmission 10 in rear transaxle casing 5 includes an alternativetransmission output shaft 20A journaling PTO shaft 26. Transmissionoutput shaft 20A is similar to transmission output shaft 20, except thattransmission output shaft 20A is extended rightward from rear transaxlecasing 5 into PTO unit casing 51B and is fixedly provided on a right endthereof with bevel gear 54 that meshes with bevel gear 55 on PTO shaft26 so as to constitute PTO gear train 50 a. In other words, PTO unit 50Cdoes not include an additional PTO input shaft but utilizes transmissionoutput shaft 20A of gear transmission 10 in rear transaxle 3 by itselfto transmit power from transmission output shaft 20A to PTO shaft 26.

Further, referring to FIG. 12, rear transaxle 3 with PTO unit 50C hasneither a parking brake, such as parking brake 60, nor a drive modeselection clutch, such as drive mode selection clutch 70. Therefore,preferably, front transaxle 2 (not shown in FIG. 12) includes a parkingbrake and a drive mode selection clutch, similar to a later-discussedfront transaxle 107 as shown in FIG. 20.

Referring to FIG. 12, gearshift clutch 21 is illustrated as including aclutch hub 91 and a gearshift sleeve 92. This illustration of gearshiftclutch 21 means that gear transmission 10 in rear transaxle 3 shown inFIG. 12 includes gearshift clutch 21 having a configuration such asshown in FIGS. 13 to 19. Moreover, gearshift clutch 21 of geartransmission 10 in rear transaxle 3 shown in FIGS. 1, 2, 10 and 11 mayhave the configuration such as shown in FIGS. 13 to 19.

Gearshift clutch 21 having a clutch guide system 90 will be describedwith reference to FIGS. 13 to 19. Referring to FIG. 13, gearshift clutch21 includes clutch hub 91 and gearshift sleeve 92. Clutch hub 91 isfixed on transmission output shaft 20 or 20A (hereinafter, “transmissionoutput shaft 20” is referred to as representative of transmission outputshafts 20 and 20A) so as to be sandwiched between a right end of axialboss 13 b of high speed forward driven gear 13 of high speed forwardgear train 10 a and a left end of axial boss 19 b of reverse driven gear19 of reverse gear train 10 c. Clutch hub 91 is formed on an outerperipheral portion thereof with splines 91 a. The right end of axialboss 13 b of high speed forward driven gear 13 is formed with splines 13a that can continue leftward from respective splines 91 a of clutch hub91 when the rotational position of gear 13 coincides to that of clutchhub 91. The left end of axial boss 19 b of reverse driven gear 19 isformed with splines 19 a that can continue rightward from respectivesplines 91 a of clutch hub 91 when the rotational position of gear 13coincides to that of clutch hub 91.

Gearshift sleeve 92 is formed on right and left inner peripheralportions thereof with right and left splines 92 aR and 92 aL,respectively. Gearshift sleeve 92 is spline-fitted at the innerperipheral portion thereof onto the outer peripheral portion of clutchhub 91 axially slidably and unrotatably relative to clutch hub 91. Inthis regard, at least either right or left splines 92 aR or 92 aL ofgearshift sleeve 92 mesh with splines 91 a of clutch hub 91 regardlessof slide of gearshift sleeve 92. A left end portion of gearshift sleeve92 is formed with an engagement portion 92 e that can mesh with pawls 15a formed on a right end of low speed forward driven gear 15.

Gearshift sleeve 92 is formed with an annular groove 92 b into which afork 93 is fitted. Fork 93 is operatively connected to a gearshift lever95 via a link 94 that may be configured mechanically or electrically(see the description of link 80 or 85 shown in FIG. 3). Due to rotationof gearshift lever 95, gearshift sleeve 92 is shiftable among fourpositions, i.e., a low speed forward position Ps1, a high speed forwardposition Ps2, a neutral position Ps3, and a reverse position Ps4.

When gearshift sleeve 92 is disposed at neutral position Ps3, both rightand left splines 92 aR and 92 aL mesh with splines 91 a of clutch hub 91and engagement portion 92 e is separated from pawls 15 a, so that alldriven gears 13, 15 and 19 disengage from gearshift sleeve 92, wherebytransmission output shaft 20 is isolated from the rotary power oftransmission input shaft 11. This state is defined as a neutral state Nof gear transmission 10.

When gearshift sleeve 92 slides rightward from neutral position Ps3 andis disposed at reverse position Ps4, left splines 92 aL mesh withsplines 91 a, right splines 92 aR mesh with splines 19 a of reversedriven gear 19, and engagement portion 92 e is separated from pawls 15a, thereby drivingly connecting transmission output shaft 20 totransmission input shaft 11 via reverse gear train 10 c. This state isdefined as a reverse driving state R of gear transmission 10.

On the other hand, when gearshift sleeve 92 slides leftward from neutralposition Ps3 and is disposed at high speed forward position Ps2, rightsplines 92 aR mesh with splines 91 a, left splines 92 aL mesh withsplines 13 a of high speed forward driven gear 13, and engagementportion 92 e is separated from pawls 15 a, thereby drivingly connectingtransmission output shaft 20 to transmission input shaft 11 via highspeed forward gear train 10 a. This state is defined as a high speedforward driving state H of gear transmission 10.

When gearshift sleeve 92 slides leftward from high speed forwardposition Ps2 and is disposed at low speed forward position Ps1, rightsplines 92 aR mesh with splines 91 a, left splines 92 aL are separatedleftward from splines 13 a of high speed forward driven gear 13, andengagement portion 92 e meshes with pawls 15 a of low speed forwarddriven gear 15, thereby drivingly connecting transmission output shaft20 to transmission input shaft 11 via low speed forward gear train 10 b.This state is defined as a low speed forward driving state L of geartransmission 10.

A configuration to locate gearshift sleeve 92 relative to clutch hub 91in the peripheral direction of transmission output shaft 20 will bedescribed with reference to FIGS. 14 to 19. Referring to FIG. 14, eachspline 92 a of gearshift sleeve 92 has a width We in the peripheraldirection thereof and is initially disposed at the exactly middleposition between every adjoining splines 91 a so as to have guide spacesS1 and S2 from adjoining splines 91 a on opposite sides thereof in theperipheral direction of gearshift sleeve 92, so that guide spaces S1 andS2 have respective widths W1 and W2 in the peripheral direction oftransmission output shaft 20 equal to each other, whereby gearshiftsleeve 92 is allowed to rotate relative clutch hub 91 until splines 92 amoving from the respective initial positions come to abut againstadjoining splines 91 a.

Referring to FIG. 15, left splines 92 aL are formed at left end portionsthereof with chamfers 92 c, and correspondingly, right end portions ofsplines 13 a are formed with chamfers 13 c. Incidentally, right splines92 aR are formed at right end portions thereof with similar chamfers,and correspondingly, left end portions of splines 19 a are formed withsimilar chamfers, although their illustration is omitted.

FIG. 15 illustrates phantom extension regions Re as defining leftwardextended portions of respective splines 91 a assumed to extend leftwardfrom their real left ends. Extension regions Re are defined as regionswhich left splines 92 aL can never enter because, even if gearshiftsleeve 92 slides leftward to engage with high speed forward driven gear13, right splines 92 aR still mesh with splines 91 a of clutch hub 91 soas to be hindered by adjoining splines 91 a from moving further in theperipheral direction.

Each clutch tooth 13 a has a width in the peripheral direction, which issubstantially equal to width We of spline 92 a (92 aL or 92 aR). Whengearshift sleeve 92 is located at its initial position relative toclutch hub 91 in the peripheral direction, each spline 92 aL is disposedat its initial position Sp1, where spline 92 aL is disposed at themiddle position between adjoining splines 91 a, so that width W1 ofguide space S1 between spline 92 aL and one of adjoining splines 91 a isequal to width W2 of guide space S2 between spline 92 aL and the otherof adjoining splines 91 a.

For convenience of description about clutch guide system 90 of gearshiftclutch 21 shown in FIG. 15, guide space S1 illustrated as being abovespline 92 aL at initial position Sp1 is referred to as “upper guidespace S1”, and the direction from spline 92 aL to guide space S1 isdefined as an “upward” direction. Guide space S2 illustrated as beingbelow spline 92 aL at initial position Sp1 is referred to as “lowerguide space S2”, and the direction from spline 92 aL to guide space S2is defined as a “downward” direction. One spline 91 a and its extensionregion Re illustrated as being above upper guide space S1 are referredto as “upper spline 91 a” and “upper extension region Re”, and anotherspline 91 a and its extension region Re illustrated as being below lowerguide space S2 are referred to as “lower spline 91 a” and “lowerextension region Re”.

At the start of leftward slide of gearshift sleeve 92 in a direction A1to engage gearshift sleeve 92 with high speed forward driven gear 13,chamfer 92 c of each left spline 92 aL may abut against chamfer 13 c ofeach spline 13 a. Once chamfer 92 c of spline 92 aL slips slightlyupward relative to chamfer 13 c of spline 13 a, chamfer 92 c slidesupward along chamfer 13 c, so that spline 92 aL slides upward againstspline 13 a in a direction A2, as spline 92 aL moves leftward indirection A1. Finally, spline 92 aL reaches an upward position Sp11between spline 13 a and upper extension region Re. Upper guide space S1has sufficient width W1 to allow the upward slide of spline 92 aL frominitial position Sp1 to upward position Sp11.

On the other hand, once chamfer 92 c of spline 92 aL slips slightlydownward relative to chamfer 13 c of spline 13 a, chamfer 92 c slidesdownward along chamfer 13 c, so that spline 92 aL slides downwardagainst spline 13 a in a direction A3, as spline 92 aL moves leftward indirection A1. Finally, spline 92 aL reaches a downward position Sp12between clutch tooth 13 a and lower extension region Re. Lower guidespace S2 has sufficient width W2 to allow the downward slide of spline92 aL from initial position Sp1 to downward position Sp12.

As mentioned above, clutch guide system 90 is defined as having threefeatures: The first feature is the chamfers formed on the splines. Inthe above-mentioned embodiment, splines 92 a of gearshift sleeve 92 areformed with chamfers 92 c, and splines 13 a of gear 13 with chamfers 13c. However, either splines 92 a of gearshift sleeve 92 or splines 13 aof gear 13 may be formed with chamfers, if the required effect can beobtained. Due to the splines provided with chamfers, splines 92 a ofgearshift sleeve 92 can be smoothly diverted from the direct axial slidedirection of gearshift sleeve 92 so as to be guided along splines 13 aof gear 13 to positions adjacent to respective splines 13 a of gear 13,even if splines 92 a of gearshift sleeve 92 abut against splines 13 a ofgear 13.

The second feature is the dimension of splines 92 a of gearshift sleeve92 relative to splines 91 a of clutch hub 91 in the peripheral directionof transmission output shaft 20, such that each spline 92 a of gearshiftsleeve 92 having width We is comparative narrow to have a sufficientguide space S1 or S2 having a width W1 or W2 between spline 92 a andspline 91 a of clutch hub 91, into which each spline 13 a of gear 13 canbe guided.

The third feature is the arrangement of splines 92 a of gearshift sleeve92 relative to splines 91 a of clutch hub 91 in the peripheral directionof transmission output shaft 20, such that each spline 92 a of gearshiftsleeve 92 dimensioned as mentioned above has sufficient guide spaces S1and S2 on both opposite sides thereof between adjoining splines 91 a ofclutch hub 91. Therefore, splines 92 a of gearshift sleeve 92 can divertin each of opposite directions relative to splines 13 a of gear 13 inthe peripheral direction so as to obtain the first and second features.The above-mentioned location of each spline 92 a at the middle positionbetween adjoining splines 91 a is one of methods for ensuring sufficientguide spaces S1 and S2 on both opposite sides of each spline 92 a.

To clarify the reason why gear guide system 90 should have the thirdfeature, i.e., why initial position Sp1 of spline 92 a should be at themiddle position between adjoining upper and lower splines 91 a so as tohave upper and lower guide spaces S1 and S2 having equal widths W1 andW2, an eccentric arrangement of spline 92 aL between adjoining upper andlower splines 91 a as shown in FIGS. 16A and 16B will be described. Inthis case, an initial position Sp2 of spline 92 aL is eccentric so as tobe adjacent to lower spline 91 a. Therefore, spline 92 aL at initialposition Sp3 and upper spline 91 a have a large space S3 therebetween.

Referring to FIG. 16A, if the position of spline 13 a of gear 13 in theperipheral direction is slightly lower than initial position Sp2 ofspline 92 aL, and once chamfer 92 c of spline 92 a of gearshift sleeve92 abuts against chamfer 13 c of spline 13 a of gear 13 and slips at atip t1 of spline 92 a slightly upward relative to tip t2 of spline 13 a,chamfer 92 c slides upward along chamfer 13 c according to the leftwardslide of gearshift sleeve 92, so that spline 92 aL slides upward againstspline 13 a in a direction A4. Finally, spline 92 aL reaches a positionSp21 adjacently above spline 13 a. In other words, such a downwardlyeccentric initial position Sp2 of spline 92 aL allows gearshift sleeve92 to rotate upward relative to spline sleeve 91 a so as to complete themeshing of left splines 92 aL of gearshift sleeve 92 with splines 13 aof gear 13.

On the contrary, referring to FIG. 16B, if the position of spline 13 ain the peripheral direction is slightly higher than initial position Sp2of spline 92 aL, and even if chamfer 92 c of spline 92 abuts againstchamfer 13 c of spline 13 a and slips slightly downward relative tospline 13 a in a direction A5, lower spline 91 a hinders chamfer 92 cfrom sliding further downward along chamfer 13 c according to theleftward slide of gearshift sleeve 92. As a result, spline 92 aL isunexpectedly held substantially at initial position Sp2, i.e., the slidelock of gearshift sleeve 92 occurs, so that gearshift sleeve 92 cannotslide to engage with gear 13.

As mentioned above, such an eccentric initial position of spline 55 abetween adjoining splines 91 a may cause the slide lock of gearshiftsleeve 92 depending on whether the chamfer of spline 13 a or 19 aslipping relative to chamfer 92 c of spline 92 a is directed to distantspline 91 a as upper spline 91 a shown in FIG. 16A or adjacent spline 91a as lower spline 91 a shown in FIG. 16B. The initial location of spline92 a at middle position Sp1 between adjoining splines 91 a isadvantageous to prevent such unexpected slide lock of gearshift sleeve92 regardless of the direction of slipping of the chamfer of spline 13 aor 19 a slipping relative to chamfer 92 c of spline 92 a.

Spline location systems 96A and 96B for initially locating gearshiftsleeve 92 relative to clutch hub 91 in the peripheral direction so as tolocate each spline 92 a at the middle position between every adjoiningsplines 91 a will now be described with reference to FIGS. 17 to 19.

Spline location system 96A will be described with reference to FIG. 17.To constitute spline location system 96A, clutch hub 91 is formed with aradial recess 91 b centripetally from the outer peripheral surfacethereof at a position corresponding to one of splines 91 a. In otherwords, when viewed in the axial direction of transmission output shaft20, all splines 91 a are aligned on the outer peripheral surface ofclutch hub 91 with a constant pitch, however, one of splines 91 a withthe constant pitch is lost, and radial recess 91 b is formed in clutchhub 91 to have its open end at the outer peripheral surface of clutchhub 91 so as to correspond to the lost spline 91 a. In this way, splines91 a and radial recess 91 b are aligned in the peripheral direction ofclutch hub 91 at regular intervals. Recess 91 b has an end surface 91 ctoward the axis of transmission output shaft 20.

Spline location system 96A includes detent pin 97 slidably fitted intoradial recess 91 b. Detent pin 97 is a sleeve having an open end 91 bfacing end surface 91 c of radial hole 91 b, and having a closed endfacing an inner peripheral portion of gearshift sleeve 92. The closedend of detent pin 97 is a hemispheric head 97 a that projectscentrifugally from the outer peripheral surface of clutch hub 91 so asto replace the lost spline 91 a. A coiled spring 98 is fitted at an endthereof into detent pin 97 via open end 97 b, and abuts at the other endthereof against end surface 91 c of radial hole 91 b, so as tocentrifugally bias detent pin 97. Therefore, in spline location system96A, spring 98 serves as a biasing device that biases detent pin 97toward the inner peripheral portion of gearshift sleeve 92, so thatdetent pin 97 serves as a pressure member pressed against the innerperipheral portion of gearshift sleeve 92.

When viewed in the axial direction of transmission output shaft 20, theinner peripheral surface of gearshift sleeve 92 among splines 92 a isformed in a circular shape, except that an inner peripheral portion 92 dof gearshift sleeve 92 between predetermined two adjoining splines 92 a(hereinafter, splines 92 a 1 and 91 a 2) having head 97 a of detent pin97 therebetween is formed in a V-shape. More specifically, innerperipheral portion 92 d of gearshift sleeve 92 is formed with a V-angleddetent recess 92 d 3 at the middle position between splines 92 a 1 and92 a 2. Inner peripheral portion 92 d of gearshift sleeve 92 is formedwith a guide surface 92 d 1 that is extended straight from angled detentrecess 92 d 3 to spline 92 a 1 so as to define guide space S1 on oneside of detent pin 97 in the peripheral direction. Inner peripheralportion 92 d of gearshift sleeve 92 is also formed with a guide surface92 d 2 that is extended straight from detent recess 92 d 3 to spline 92a 2 so as to define guide space S2 on the other side of detent pin 97 inthe peripheral direction.

Head 97 a of detent pin 97 is initially located at a position Sp0 wherehead 97 a of detent pin 97 is pressed onto detent recess 92 d 3 at themiddle position between splines 92 a 1 and 92 a 2. This rotational angleof gearshift sleeve 92 relative to clutch hub 91, where head 97 a ofdetent pin 97 contacts detent recess 92 d 3, is defined as an initialrotational angle Sp1 of gearshift sleeve 92 relative to clutch hub 91.Even if gearshift sleeve 92 rotates relative to clutch hub 91 so as todeviate from its initial rotational angle Sp1 relative to clutch hub 91so that head 97 a of detent pin 97 is pressed against either guidesurface 92 d 1 or 92 d 2, gearshift sleeve 92 can return to initialrotational angle Sp1 relative to clutch hub 91 due to the centrifugalforce of spring 98 biasing head 97 a of detent pin 97 toward detentrecess 92 d 3. Guide surface 92 d 1 or 92 d 2 functions to guide head 97a toward detent recess 92 d 3. Incidentally, this centrifugal force ofspring 98 is enhanced by rotating transmission output shaft 20, so thatthe effect of spline location system 98A for biasing gearshift sleeve 92to initial rotational angle Sp1 relative to clutch hub 91 is enhancedduring traveling of the vehicle.

Spline location system 96B will be described with reference to FIGS. 18and 19. In this regard, an outer peripheral portion of a right or left(in this embodiment, right) end boss portion of gearshift sleeve 92 ispartly expanded tangently with respect to the axis of transmissionoutput shaft 20 so as to form a support portion 92 f having a throughhole 92 h extended in the radial direction of transmission output shaft20. Through hole 92 h has inner and outer open ends. A cap 99 is fittedinto through hole 92 h so as to close the outer open end of through hole92 h, so that through hole 92 h closed at the outer open end by cap 99serves as a recess having an open end at the inner peripheral portion ofgearshift sleeve 92. Detent pin 97 is fitted into through hole 92 h soas to have head 97 a projecting toward clutch hub 91 via the inner openend of through hole 92 h. Spring 98 is interposed between detent pin 97and an inner end surface 99 a of cap 99 in hole 97 b so as tocentripetally bias head 97 a of detent pin 97 toward the axis oftransmission output shaft 20. An inner peripheral portion 92 g ofgearshift sleeve 92 having hole 92 h at the middle portion thereof inthe peripheral direction is expanded centripetally toward the outerperipheral surface of clutch hub 91.

Since gearshift sleeve 92 is formed with support portion 92 f andexpanded inner peripheral portion 92 d at the right end boss portionthereof, the open end of hole 92 h are aligned with right splines 92 aRof gearshift sleeve 92. When viewed in the axial direction oftransmission output shaft 20, all right splines 92 aR are aligned on theouter peripheral surface of clutch hub 91 with a constant pitch,however, two of right splines 92 aR with the constant pitch are lost,and opposite ends of expanded inner peripheral portion 92 g in theperipheral direction of transmission output shaft 20 are defined by twolost right splines 92 aR or two corresponding left splines 92 aL (asdrawn in phantom lines in FIG. 19). Therefore, detent pin 97 is disposedat the middle position between the lost two of right splines 92 aR withthe constant pitch.

When viewed in the axial direction of transmission output shaft 20, theouter peripheral surface of clutch hub 91 among splines 91 a is formedin a circular shape, except that the outer peripheral portion of clutchhub 91 is partly scooped out to form a shallow V-shape recessed outerperipheral portion 91 d. A deepest portion of recess 91 d is curved orobtusely angled so as to serve as an angled detent recess 91 d 3. In theaxial view, all splines 91 a are aligned on the outer peripheral surfaceof clutch hub 91 with a constant pitch, however, one of splines 91 awith the constant pitch is lost, and detent recess 91 d 3 is disposed atthe position corresponding to the lost spline 91 a. Therefore, twosplines 91 a 1 and 91 a 2 having detent recess 91 d 3 therebetween arepredetermined as neighboring the lost spline 91 a corresponding todetent recess 91 d 3 on opposite sides of detent recess 91 d 3 in theperipheral direction of transmission output shaft 20, and these splines91 a 1 and 91 a 2 have equal distances from detent recess 91 d 3,equaling the above-mentioned constant pitch of splines 91 a. In otherwords, detent recess 91 d 3 is disposed at the middle position betweenadjoining splines 91 a 1 and 91 a 2 in the peripheral direction oftransmission output shaft 20.

Shallow V-shape recessed outer peripheral portion 91 d of clutch hub 91has opposite ends in the peripheral direction of transmission outputshaft 20 between detent recess 91 d 3 and one adjoining spline 91 a 1,and between detent recess 91 d 3 and the other adjoining spline 91 a 2,respectively. When head 97 a of detent pin 97 is located at detentrecess 91 d 3, the opposite ends of recessed outer peripheral portion 91d are located to correspond to the opposite ends of expanded innerperipheral portion 92 g in the peripheral direction of transmissionoutput shaft 20. One half of recessed outer peripheral portion 91 dbetween detent recess 91 d 3 and one end of recessed outer peripheralportion 91 d close to spline 91 a 1 is formed as a guide surface 91 d 1,and the other half of recessed outer peripheral portion 91 d betweendetent recess 91 d 3 and the other end of recessed outer peripheralportion 91 d close to spline 91 a 2 is formed as a guide surface 91 d 2.In other words, guide surfaces 91 d 1 and 91 d 2 are formed at the outerperipheral portion of clutch hub 91 between angled detent recess 91 d 3and one predetermined spline 91 a 1, and between angled detent recess 91d 3 and the other predetermined spline 91 a 2.

Head 97 a of detent pin 97 is initially located at a position Sp0 wherehead 97 a of detent pin 97 is pressed onto detent recess 91 d 3 at themiddle position between adjoining splines 91 a 1 and 91 a 2. Thisrotational angle of gearshift sleeve 92 relative to clutch hub 91, wherehead 97 a of detent pin 97 contacts detent recess 91 d 3, is defined asinitial rotational angle Sp1 of gearshift sleeve 92 relative to clutchhub 91. Even if gearshift sleeve 92 rotates relative to clutch hub 91 soas to deviate from initial rotational angle Sp1 relative to clutch hub91 so that head 97 a of detent pin 97 is pressed against guide surface91 d 1 or 91 d 2, gearshift sleeve 92 can return to initial rotationalangle Sp1 relative to clutch hub 91 due to the centripetal force ofspring 98 biasing head 97 a of detent pin 97 toward detent recess 91 d3. Guide surface 91 d 1 or 91 d 2 functions to guide head 97 a towarddetent recess 91 d 3.

In comparison with spline location system 96A, spline location system96B is advantageous for maintenance of detent pin 97 and spring 98because detent pin 97 and spring 98 can easily accessed only by removingcap 99 outward from through hole 92 h in gearshift sleeve 92 disposedoutside of clutch hub 91.

An alternative four-wheel drive vehicle 100 equipped with an alternativetransmission system will be described with reference to FIGS. 20 to 29.Vehicle 100 is equipped with a power unit 101 that is an assemblyincluding an engine 102, a belt-type continuously variable transmission(hereinafter, referred to as “CVT”) 103 serving as a main speed-changingtransmission, and a gear transmission 104 serving as a subspeed-changing transmission and a reverser, i.e., a device for selectingeither forward or backward traveling direction of vehicle 100.

A rear transaxle 105 for driving right and left rear wheels 106 issupported at a rear portion of vehicle 100. A front transaxle 107 fordriving right and left front wheels 108 is supported at a rear portionof vehicle 100. An output power of power unit 101 is distributed betweenrear and front transaxles 105 and 107 so as to drive four wheels, i.e.,rear wheels 206 and front wheels 108. Each rear wheel 106 is providedwith a brake 106 b, and each front wheel 108 is provided with a brake108 b.

Referring to FIG. 20, power unit 101 will be described in detail. Powerunit 101 includes a transmission casing 110. A front portion oftransmission casing 110 is formed as a CVT housing 110 a of CVT 103, anda rear portion of transmission casing 110 is formed as a geartransmission housing 110 b of gear transmission 104. Gear transmissionhousing 110 b is disposed rightward or leftward (in this embodiment,leftward) from engine 102. A right portion of CVT housing 103 isextended rightward in front of engine 102. A fore-and-aft horizontalengine output shaft 111 is extended forward from engine 102 into theright portion of CVT housing 110 a. The portion of engine output shaft111 in the right portion of CVT housing 110 a serves as a drive pulleyshaft having a drive pulley 112 thereon.

Gear transmission 104 includes four fore-and-aft horizontal rotaryshafts, i.e., a transmission input shaft 115, a transmission countershaft 116, an idle shaft 117, a reduction shaft 118, and a transmissionoutput shaft 119. These rotary shafts 115, 116, 117, 118, and 119 areextended parallel to one another, and are journalled in geartransmission casing 110 b. Transmission input shaft 115 is extendedforward from gear transmission housing 110 a into a left portion of CVThousing 110 a. The portion of transmission input shaft 115 in the leftportion of CVT housing 110 a serves as a driven pulley shaft having adriven pulley 114 thereon. A belt 113 is looped over drive pulley 112and driven pulley 114, thereby constituting belt-type CVT 103.

In gear transmission housing 110 b, gear transmission 104 includes ahigh speed forward gear train 120, a low speed forward gear train 121,and a reverse gear train 122, which are interposed parallel to eachother between transmission input shaft 115 and transmission countershaft 116. Gear trains 120, 121 and 122 have respective drive gearsfixed on transmission input shaft 115, and respective driven gearsprovided on transmission output shaft 116 rotatably relative totransmission output shaft 116. More specifically, the driven gear of lowspeed forward gear train 121 is fitted on an axial boss portion of thedriven gear of high speed forward gear train 120 so as to be rotatablerelative to the driven gear of high speed forward gear train 120. Thedrive gears of forward gear trains 120 and 121 directly mesh with therespective driven gears, and the drive gear of reverse gear train 122meshes with the corresponding driven gear via an idle gear on idle shaft117.

A shifter 123 is provided on transmission counter shaft 116 so as toselectively engage with one of the driven gears to transmit power fromtransmission input shaft 115 to transmission counter shaft 116 viaselected one of gear trains 120, 121 and 122. Shifter 123 may be aclutch shifter like gearshift clutch 21, or a synchromesh shifter.

Alternatively, shifter 123 may be provided on transmission input shaft115, drive gears of gear trains 120, 121 and 122 may be provided ontransmission input shaft 115 rotatably relative to transmission inputshaft 115, and driven gears of gear trains 120, 121 and 122 may be fixedon transmission counter shaft 118.

A reduction gear train 124 is interposed between transmission countershaft 116 and transmission output shaft 119 via reduction shaft 118.More specifically, reduction gear train 124 includes four gears, i.e., adiametrically small gear fixed on transmission counter shaft 116, adiametrically large gear fixed on reduction shaft 118, a diametricallysmall gear fixed on reduction gear 118, and a diametrically large gearfixed on transmission output shaft 119. The diametrically small gear ontransmission counter shaft 116 directly meshes with the diametricallylarge gear on reduction shaft 118, and the diametrically large gear onreduction shaft 118 directly meshes with diametrically large gear ontransmission output shaft 119.

Rear transaxle 105 includes a rear transaxle casing 105 a, an inputshaft 128, a bevel pinion 129, a bevel bull gear 130, and an outputshaft 130. Rear transaxle casing 105 a journals fore-and-aft horizontalinput shaft 128 and laterally horizontal output shaft 131 therein. Inrear transaxle casing 105 a, bevel pinion 129 is fixed (or formed) on arear end of input shaft 128, and bevel bull gear 130 is fixed on alaterally intermediate portion of output shaft 131. Right and left endportions of output shaft 131 project rightward and leftward from reartransaxle casing 105 a, and are drivingly connected to axles 106 a ofright and left rear wheels 106 via respective proximal universal joints132, propeller shafts 133 and distal universal joints 134.

A connection shaft housing 110 c is interposed between a rear end ofgear transmission housing 110 b and a front end of rear transaxle casing105 a. Transmission output shaft 119 of gear transmission 104 of powerunit 101 is extended rearward from the rear end of gear transmissionhousing 110 b so as to have its rear end in shaft housing 110 c. Inputshaft 128 of rear transaxle 105 is extended forward from the front endof rear transaxle casing 105 a so as to have its front end in shafthousing 110 c. In shaft housing 110 c, a fore-and-aft horizontalconnection shaft 126 is coaxially extended between transmission outputshaft 119 and input shaft 128. Connection shaft 126 is connected atfront and rear ends thereof to the rear end of transmission output shaft119 and the front end of input shaft 128 via respective couplings 125and 127, e.g., spline sleeves.

Transmission output shaft 119 of gear transmission 104 is extendedforward from gear transmission housing 110 b and is passed through CVThousing 110 a so as to have its front end forward from a front end ofCVT housing 110 a. A propeller shaft 136 is drivingly connected at arear end thereof to the front end of transmission output shaft 119 via auniversal joint 135, and at a front end thereof to a rear end of alater-discussed input shaft 138 (more specifically, a later-discussedclutch input shaft 138 a) via a universal joint 137.

Front transaxle 107 includes a front transaxle casing 107 a. Fronttransaxle casing 107 a incorporates a differential unit 143, andjournals right and left differential output shafts 145 of differentialunit 143. Differential unit 143 includes a bevel input gear 144 meshingwith a bevel pinion 142 fixed (or formed) on a front end of input shaft138 (more specifically, a later-discussed clutch output shaft 138 b), sothat differential unit 143 distributes the rotary power bevel input gear144 driven by input shaft 138 between right and left differential outputshafts 145.

Right and left differential output shafts 145 project rightward andleftward from front transaxle casing 107 a, and are drivingly connectedto axles 108 a of right and left front wheels 108 via respectiveproximal universal joints 146, propeller shafts 147 and distal universaljoints 148. Differential unit 143 is a limited slip differential unitthat limits a differential rotatability of right and left differentialoutput shafts 145. Therefore, if one of right and left front wheels 108is going to be stuck, differential unit 143 distributes a part ofdriving torque of the other front wheel 108 to front wheel 108 beingstuck, thereby preventing vehicle 100 from being stuck.

Front transaxle 107 is provided with a clutch unit 139 including a drivemode selection clutch 140 and a parking brake 141. Clutch unit 139 willnow be described with reference to FIGS. 21 to 25. Clutch unit 139includes a clutch unit casing 139 a. Clutch unit casing 139 a includes amain housing 139 b, a clutch operation system housing 139 c, and a brakeoperation system housing 139 d. Clutch operation system housing 139 c isjoined to an upper front portion of main housing 139 b, and brakeoperation system housing 139 d is joined to a lower front portion ofmain housing 139 b, so that housings 139 b, 139 c and 139 d are joinedtogether to constitute clutch unit casing 139 a.

Main housing 139 b is formed at a front end thereof with a flange. Thisflange is fastened to a rear end of front transaxle casing 107 a viabolts 179 so that clutch unit casing 139 a is extended rearward fromfront transaxle casing 107 a. Main housing 139 b journals input shaft138. Input shaft 138 includes rear clutch input shaft 138 a and frontclutch output shaft 13 8 b extended coaxially to each other. The rearend portion of clutch input shaft 138 a projects rearward from a rearend of main housing 139 b of clutch unit casing 139 a so as to bedrivingly connected to transmission output shaft 119 of power unit 101via propeller shaft 136 with universal joints 135 and 137 as mentionedabove. The front end portion of clutch output shaft 138 b projectsforward from the front end of main housing 139 b into front transaxlecasing 107 a so that bevel pinion 142 on the front end of clutch outputshaft 138 b meshes with bevel bull gear 144 of differential unit 143.

Referring to FIG. 23, the inside space of main housing 139 b is dividedinto a front clutch chamber 139 e incorporating drive mode selectionclutch 140 and a rear brake chamber 139 f incorporating parking brake141. In clutch chamber 139 e, a projection 138 a 1 formed on a front endof clutch input shaft 138 a is fitted into a recess 138 b 1 formed in arear end portion of clutch output shaft 138 b so that the front endportion of clutch input shaft 138 a and the rear end portion of clutchoutput shaft 138 b are joined to each other so as to allow clutch inputand output shafts 138 a and 138 b to rotate relative to each other.

In clutch chamber 139 e, the front end portion of clutch input shaft 138a and the rear end portion of clutch output shaft 138 b are formed onouter peripheral surfaces thereof with splines, and a clutch sleeve 140a is formed on an inner peripheral surface thereof with splines. Clutchsleeve 140 a is constantly spline-fitted on the front end portion ofclutch input shaft 138 a so as to be axially slidable along clutch inputshaft 138 a between a clutch-off position Pc12 and a clutch-on positionPc12.

When clutch sleeve 138 a is disposed at clutch-off position Pc11, afront end portion of clutch sleeve 140 a is disposed on the front endportion of clutch input shaft 138 a so as to be separated from the rearend portion of clutch output shaft 138 b, thereby keeping clutch outputshaft 138 b free from a rotary power of clutch input shaft 138 a.Therefore, the output power of power unit 101 is transmitted to rearwheels 106 but is not transmitted to front wheels 108, so that vehicle100 travels in 2WD mode. When clutch sleeve 138 a slides forward fromclutch off position 301 and is disposed at clutch-on position Pc12, thefront end portion of clutch sleeve 138 a is also spline-fitted onto therear end portion of clutch output shaft 13 8 b so as to rotatablyintegrate clutch output shaft 13 8 b with clutch input shaft 138 a.Therefore, the output power of power unit 101 is distributed to all fourwheels 106 and 108 so that vehicle 100 travels in 4WD mode.

Referring to FIGS. 21 and 22, a clutch operation system 180 is disposedin clutch operation system housing 139 c. Clutch operation system 180includes a vertical clutch operation shaft 182, which is journalled byclutch operation system housing 139 c and projects upward from a top ofclutch operation system housing 139 c. Vehicle 100 is equipped with adrive mode selection lever 187 serving as a manipulator for selectingeither the 2WD or 4WD mode for traveling of vehicle 100. Drive modeselection lever 187 is operatively connected to clutch operation shaft182 via a link 181 outside of clutch unit casing 139 a. Link 181 mayhave any configuration. It may be a mechanical link, e.g., a wire and/ora rod, or an electric link, e.g., an electric actuator or combination ofan electric actuator and gears.

In clutch unit casing 138, clutch operation system 180 includes avertical clutch sleeve operation shaft 184 interlocking with clutchoperation shaft 182 via an arm or the like. A bottom end of clutchsleeve operation shaft 184 is fitted into an annular groove 140 b formedon clutch sleeve 140 a. By operating drive mode selection lever 187,clutch operation shaft 182 rotates centered on its own vertical axis, sothat clutch sleeve operation shaft 184 revolves centered on the verticalaxis of clutch operation shaft 182. During the revolution of clutchsleeve operation shaft 184, clutch sleeve operation shaft 184 moves inthe fore-and-aft direction so as to push clutch sleeve 140 a forward orrearward between clutch-off position Pc11 and clutch-on position Pc12.

Referring to FIGS. 21 to 25, in brake chamber 139 f, parking brake 141is configured so as to brake clutch input shaft 138 a. Parking brake 141provided in clutch unit 139 attached to front transaxle 107 in vehicle100 is configured to has such a compact cam mechanism (a later-discussedbrake operation system 190) to solve the problem stated regarding thebackground art disclosed by JP 2004-082926 A.

Parking brake 141 includes a flange member 149, a brake arm member 150,and a cam arm member 151. In this regard, clutch input shaft 138 a isformed on an outer peripheral surface thereof with splines in brakechamber 139 f Flange member 149, which is spline-fitted on clutch inputshaft 138 a axially slidably and unrotatably relative to clutch inputshaft 138 a. Flange member 149 is formed at a rear end thereof with avertical surface 149 a from which outer peripheral edges serving aspawls 149 b are extended rearward. Pawls 149 b are aligned in theperipheral direction of clutch input shaft 138 a, preferably, at regularintervals (in this embodiment, four pawls 149 b are formed to have fournotches 149 b at 90 degrees' intervals) when viewed in the axialdirection of clutch input shaft 138 a, so as to have notches 149 cthereamong. In this regard, bottoms of notches 149 b among pawls 149 bare defined by vertical surface 149 a of flange member 149.

Brake arm member 150 and cam arm member 151 will be described on theassumption that brake arm member 150 and cam arm member 151 are disposedleftward from cam input shaft 138 a in brake chamber 139 f as shown inFIGS. 23 to 25. Brake arm member 150 is integrally formed to include ahorizontal plate-shaped arm 150 a, a pawl 150 b extended leftward from aright end portion of arm 150 a, a boss 150 c open at the right endportion of arm 150 a and extended vertically downward from the right endportion of arm 150 a, and a vertical cam pin 150 d projecting upwardfrom a left end portion of arm portion 150 a. Cam arm member 151 isintegrally formed to include a horizontal plate-shaped cam arm 151 a, aboss 151 b open at a rear end portion of cam arm 151 a and extendedupward from a rear end portion of cam arm 151 a, and an arm 151 cextended horizontally from an upper portion of boss 151 b. Cam arm 151 ais formed in a front end portion thereof with a cam hole 157 including alocking area 164 and an unlocking area 165. Locking area 164 andunlocking area 165 are angled from each other, and joined to each otherso as to form cam hole 157 in a V-shape.

In brake chamber 139 f, cam arm member 151 is disposed rearward from arm150 a of brake arm member 150. Vertical cam pin 150 d of brake armmember 150 is provided on the outer peripheral surface thereof with acollar 156 and is inserted with collar 156 upward into cam hole 157 ofarm 151 a. Vertical pivot shafts (not shown) are provided in brakechamber 139 f and are passed through respective bosses 150 c and 151 b,so that brake arm member 150 is rotatable centered on a vertical axis C1of the pivot shaft passed through boss 150 c, and cam arm member 151 isrotatable centered on a vertical axis C2 of the pivot shaft passedthrough boss 151 b. In this way, brake arm member 150 and cam arm member151 are assembled together to constitute brake operation system 190shown in FIG. 21.

Referring to FIG. 21, the upper portion of boss 151 b of cam arm member151 formed with arm 151 c projects upward from a top of brake operationsystem housing 139 d. Vehicle 100 is equipped with a parking brake lever189 serving as a manipulator for selecting either an unbraking orbraking state of parking brake 141. Parking brake lever 189 isoperatively connected to arm 151 c via a link 188 outside of clutch unitcasing 139. Link 188 may have any configuration. It may be a mechanicallink, e.g., a wire and/or a rod, or an electric link, e.g., an electricactuator or combination of an electric actuator and gears.

According to rotational operation of parking brake lever 189, cam armmember 151 rotates centered on vertical axis C2. Accordingly, cam arm151 a of cam arm member 151 rotates to function as a cam to cam pin 150d of brake arm member 150 in cam hole 157 of cam arm 151 a, so that campin 150 d is switched between locking area 164 and unlocking area 165 ofcam hole 157, thereby rotating brake arm member 150 centered on verticalaxis C1 so as to switch pawl 150 b between a braking position andunbraking position.

Referring to FIG. 23, pawl 150 b set at the unbraking position isdisposed away from notch 149 c so as to disengage from flange member149, thereby allowing rotation of clutch input shaft 138 a driven by theoutput power of transmission output shaft 119 of power unit 101. In thisstate, if clutch sleeve 140 a is set at clutch-on position Pc12, therotation of clutch input shaft 138 a is transmitted to front wheels 108via clutch output shaft 138 b and differential unit 143.

On the other hand, referring to FIG. 24, pawl 150 b set at the brakingposition is fitted into notch 149 c so as to engage with pawls 150 b offlange member 149, thereby braking clutch input shaft 138 a. The brakingforce applied onto clutch input shaft 138 a is transmitted totransmission output shaft 119 of power unit 101, thereby braking rearwheels 106. In this state, if clutch sleeve 140 a is set at clutch-onposition Pc12, the braking force applied onto clutch input shaft 138 ais transmitted to clutch output shaft 138 b and differential unit 143,thereby braking front wheels 108.

The cam function of brake operation system 190 to switch pawl 150 b ofbrake arm member 150 between the braking position and the unbrakingposition will be described in detail with reference to FIGS. 23, 24 and25. In this regard, it should be noticed that FIGS. 23, 24 and 25 arebottom views so that the illustrated right-and-left direction of brakeoperation system 190 is opposite the actual right-and-left directionthereof. This thing is adapted to description of alternative embodimentswith reference to FIG. 27.

The location of pawl 150 b at the unlocking position depends on therotation of brake arm member 150 in an unbraking direction D1 a centeredon axis C1. The rotation of brake arm member 150 in unbraking directionD1 a is caused by shifting cam pin 150 d with collar 156 thereon from abraking position P1 b in braking area 164 of cam hole 157 to anunbraking position P1 a in unbraking area 165 of cam hole 157. The shiftof cam pin 150 d from braking position P1 b to unbraking position P1 ais caused by rotating cam arm member 151 in an unbraking direction D2 afrom a braking rotational position P2 b to an unbraking rotational angleP2 a.

On the other hand, the location of pawl 150 b at the locking positiondepends on the rotation of brake arm member 150 in a braking directionD1 b centered on axis C1. The rotation of brake arm member 150 inbraking direction D1 b is caused by shifting cam pin 150 d fromunbraking position P1 a in unbraking area 165 to braking position P1 bin braking area 164. The shift of cam pin 150 d from unbraking positionP1 a to braking position P1 b is caused by rotating cam arm member 151in a braking direction D2 b from unbraking rotational angle P2 a tobraking rotational angle P2 b.

Cam arm 151 a of cam arm member 151 is formed with a right front edge157 a, a right rear edge 157 b, and a right end edge 157 e connecting aright end of right front edge 157 a to a right end of right rear edge157 b, so that right front edge 157 a, right rear edge 157 b and rightend edge 157 e define braking area 164 as a right area of cam hole 157.On the other hand, cam arm 151 a of cam arm member 151 is formed with aleft front edge 157 c, a left rear edge 157 d, and a left end edge 157 fconnecting a left end of left front edge 157 c to a left end of leftrear edge 157 d, so that left front edge 157 c, left rear edge 157 d andleft end edge 157 f define unbraking area 165 as a left area of cam hole157.

When cam arm member 151 is disposed at braking rotational angle P2 b andcam pin 150 d is disposed at braking position P1 b, as shown in FIGS. 24and 25, right front edge 157 a defining braking area 164 of cam hole 157is extended exactly in the lateral direction perpendicular to the axialdirection of clutch input shaft 138 a. A lateral line L1 drawn in FIG.24 defines this lateral direction. Left front edge 157 c definingunbraking area 165 of cam hole 157 is extended forwardly leftwardslantwise from a joint point of right and left front edges 157 a and 157c. On the other hand, when cam arm member 151 is disposed at unbrakingrotational angle P2 a and cam pin 150 d is disposed at unbrakingposition P1 a, right front edge 157 a is extended leftwardly forwardslantwise with respect to lateral line L1, i.e., the exact lateraldirection perpendicular to the axial direction of clutch input shaft 138a.

Further, when cam arm member 151 is disposed at braking position P2 band cam pin 150 d is disposed at braking rotational angle P1 b, as shownin FIGS. 24 and 15, axis C1 of cam pin 150 d at braking position P1 b isdisposed forward from rotary axis C2 of cam arm 151 a so that axes C1and C2 are aligned in a fore-and-aft line parallel to the axialdirection of clutch input shaft 138 a. This fore-and-aft line isreferred to a retaining force activation line Lf.

Pawl 150 b disposed at the braking position is inserted forward intonotch 149 c so as to abut at a front end thereof against verticalsurface 149 a of flange member 149 as the bottom surface of notch 149 c,thereby receiving a rearward counterforce Tf1. This rearwardcounterforce Tf1 onto pawl 150 b functions as a rotational force inunbraking direction D1 a to brake arm member 150, and this rotationalforce of brake arm member 150 in unbraking direction D1 a functions as aforward thrusting force Tf2 pressing a front end portion 156 a of collar156 on cam pin 150 d at braking position P1 b in braking area 164against right front edge 157 a of cam arm 151 a.

Forward thrusting force Tf2 is directed on retaining force activationline Lf, and right front edge 157 a is extended along exact lateral lineL1 as mentioned above, so that right front edge 157 a receives fullforward thrusting force Tf2 without diverting so as to surely retain campin 150 d at braking position P1 b. Therefore, counterforce Tf1 offlange member 149 just functions as resistance against rotation of camarm member 151 centered on vertical axis C2. As a result, cam arm member151 is stably held at braking rotational angle P2 b so as to stably holdcam pin 150 d at braking position P1 b and the engagement of pawl 150 bwith flange member 149.

Incidentally, collar 156 may not be provided on cam pin 150 d if anouter peripheral surface of cam pin 150 d has a sufficient endurance. Inthis case, a front end portion of cam pin 150 d directly abuts againstright or left front edge 157 a or 157 c. A surface of collar 156 or campin 150 d contacting right or left front edge 157 a or 157 c can haveany area or any shape.

Further, axis C2 may be allowed to deviate within a tolerance width Wtrightward or leftward from the fore-and-aft line as retaining forceactivation line Lf extended rearward from axis C1 of cam pin 150 b atbraking position P1 b. Preferably, tolerance width Wt is not more than15% of a distance D between axes C1 and C2. Further, right front edge157 a of cam arm 150 a defining braking area 164 of cam hole 157 may beallowed to slant within a tolerance angle At forward or rearward fromlateral line L1. Preferably, tolerance angle At is not more than 10°.Such threshold width Wt and angle At are determined so as to preventforward thrusting force Tf2 from activating as a force to thrust cam pin150 d in the lateral direction so as to unexpectedly guide cam pin 150 dinto unbraking area 165 of cam hole 157.

As understood from the above-mentioned description, to shift pawl 150 bfrom the unbraking position to the braking position, cam arm member 151is rotated in braking direction 167 from unbraking rotational angle 158to braking rotational angle 159. During the rotation of cam arm member151 from unbraking rotational angle 158 to braking rotational angle 159,the front portion of cam arm 151 a at right front edge 157 a, and then,at left front edge 157 c, pushes cam pin 150 b with collar 156 rearward,thereby rotating arm 150 a in braking direction 170 centered on axis 152a of pivot shaft 152. Accordingly, cam pin 150 b with collar 156 movesfrom unbraking area 165 of cam hole 157 into braking area 164 of camhole 157. Collar 156 on cam pin 150 b comes to abut against right frontedge 157 a, right rear edge 157 b and right end edge 157 e so that campin 150 b is located at braking position P1 b, whereby pawl 150 breaches its braking position, i.e., is fitted into notch 149 c so as toengage with flange member 149. Afterward, pawl 150 b receives rearwardcounterforce 161 from flange member 149, so that collar 156 on cam pin150 d at braking position P1 b is pressed against right front edge 157 aby forward thrusting force Tf2 caused by counter force Tf1 from flangemember 149, so that brake arm member 150 and cam arm member 151 aresurely held at their braking positions.

To shift pawl 150 b from the braking position to the unbraking position,cam arm member 151 is rotated in unbraking direction D2 a from brakingrotational angle P2 b to unbraking rotational angle P2 a. During therotation of cam arm member 151 from braking rotational angle P2 b tounbraking rotational angle P2 a, the front portion of cam arm 151 apushes cam pin 150 b with collar 156 forward at right rear edge 157 b,and then, at left rear edge 157 d, thereby rotating arm 150 a inunbraking direction D1 a centered on axis C2. Accordingly, cam pin 150 bwith collar 156 moves from braking area 164 of cam hole 157 intounbraking area 165 of cam hole 157. Collar 156 on cam pin 150 b comes toabut against left front edge 157 c, left rear edge 157 d and left endedge 157 f so that cam pin 150 b is located at unbraking position P1 a,whereby pawl 150 b reaches its unbraking position, i.e., is releasedfrom notch 149 c so as to disengage from flange member 149.

Referring to FIGS. 26 and 27, an alternative clutch unit 239 to beattached to front transaxle 107 is similar to clutch unit 139 exceptthat clutch unit 239 is configured so as to incorporate an alternativeparking brake 241. Clutch unit 239 includes a clutch unit casing 242.Clutch unit casing 242 includes a main housing 243, and an upper housing244 joined to an upper portion of main housing 243. Main housing 243journals input shaft 238, i.e., a clutch input shaft 237 and an unshownclutch output shaft coaxially joined to each other similarly to clutchinput shafts 138 a and 138 b. Clutch unit casing 242 is formed thereinwith a front clutch chamber 242 a and a rear brake chamber 242 b,similar to clutch chamber 139 e and brake chamber 139 f in clutch unitcasing 139 a. In brake chamber 242 b, an inner peripheral portion ofmain housing 243 of clutch unit casing 242 is formed with engagementrecesses 242 c.

Parking brake 241 includes a brake flange 212 and a brake shift sleeve213, and is provided with a cam mechanism including a cam 210 foroperating brake shift sleeve 213. Brake flange 212 is formed withengagement projections 212 a radially centrifugally from an outerperipheral edge of brake flange 212. Engagement projections 212 a arefitted into respective engagement recesses 242 c so as to fix brakeflange 212 to main housing 243 of clutch unit casing 242. In thisregard, when viewed in the axial direction of input shaft 238, theengagement of engagement projections 212 a to clutch unit casing 242 maybe similar to the later-discussed engagement of engagement projections349 of a brake flange 329 to a clutch unit casing 342, although FIG. 26does not illustrate it.

An inner peripheral surface 212 c of brake flange 212 is spaced from thesplined outer peripheral portion of clutch input shaft 237, so that anannular space is provided between inner peripheral surface 212 c ofbrake flange 212 and the splined outer peripheral portion of clutchinput shaft 237. A rear inner peripheral portion of brake flange 212 isstepped, and is formed with pawls 213 b. Brake shift sleeve 213 isstepped at an axially (fore-and-aft) intermediate portion thereof so asto have a radially thin front portion and a radially thick rear portion.The axially intermediate portion of brake shift sleeve 213 is formedwith pawls 213 a adapted to engage with pawls 212 b of brake flange 212.

The radially thin front portion of brake shift sleeve 213 is defined asa guide portion 213 b whose inner peripheral portion is splined. Guideportion 213 b of brake shift sleeve 213 is passed through the annularspace defined by inner peripheral surface 212 c of brake flange 212, andis spline-fitted onto the splined outer peripheral portion of clutchinput shaft 237, so that brake shift sleeve 213 is axially(fore-and-aft) slidable and unrotatable relative to clutch input shaft237. Pawls 213 a of brake shift sleeve 213 are engaged with pawls 212 bof brake flange 212 by sliding brake shift sleeve 213 forward, and aredisengaged from pawls 212 b of brake flange 212 by sliding brake shiftsleeve 213 rearward.

A bearing 271 is fitted on clutch input shaft 237 so as to partitionbrake chamber 242 b from clutch chamber 242 a. A wave washer 214 isprovided around clutch input shaft 237 between bearing 271 and a frontend of guide portion 213 b of brake shift sleeve 213. Wave washer 214has an elastic force that biases brake shift sleeve 213 rearward, i.e.,in an unbraking direction Ds.

The radial thick portion of brake shift sleeve 213 is further radiallyexpanded at a rear end thereof in a flange-like shape so as to have avertical rear end surface 213 c. Cam 210 is disposed leftward fromclutch input shaft 237 and rearward from rear end surface 213 c of brakeshift sleeve 213. Cam 210 includes upper and lower cam plates 211 and avertical camshaft 206. Upper housing 244 is formed with an upper bossportion 244 a having a vertical boss hole 244 b, and main housing 243 isformed at a bottom portion thereof with a lower boss portion 243 ahaving a vertical boss hole 243 b. Vertical camshaft 206 is passed at anupper portion thereof through boss hole 244 b, and at a lower portionthereof through boss hole 243 b. Upper cam plate 211 is fixed oncamshaft 206 adjacently to a horizontal flat lower end surface 244 c ofupper boss portion 244. Lower cam plate 211 is fixed on camshaft 206adjacently to a horizontal flat upper end surface 243 c of lower bossportion 243 a. Therefore, upper and lower horizontal surfaces 244 c and243 c hinder upper and lower cam plates 206 from moving upward ordownward, thereby keeping cam 210 from deviating in the verticaldirection.

Vertical camshaft 206 is supported by upper and lower boss portions 244a and 233 a of clutch unit casing 242 so as to be slidably rotatablecentered on its own vertical axis C4. While lower boss portion 243 a isformed to close a bottom end of lower boss hole 243 b, upper boss hole244 b is open at a top end surface of clutch unit casing 242 (i.e.,upper housing 244), so that an upper portion of camshaft 206 projectsupward from the top end surface of clutch unit casing 242, and is formedwith an annular groove 207 adjacent to the top end surface of clutchunit casing 244. A retaining plate 215 is fastened onto the top endsurface of upper housing 244 via at least one bolt 216, and is partlyfitted into annular groove 207 so as to prevent camshaft 206 fromupwardly escaping.

The upper portion of camshaft 206 is operatively connected to parkingbrake lever 189 via link 188, similar to those for parking brake 141. Inthis regard, by rotational operating parking brake lever 189, camshaft206 is rotationally shiftable between an unbraking rotational angle P4 aand a braking rotational angle P4 b.

A bottom portion of clutch unit casing 242, i.e., main housing 243, isbored by a lateral horizontal hole 243 d. One end of hole 243 d is openat an outer side surface of clutch unit casing 242, and the other end ofhole 243 d is open at an inner peripheral surface of boss portion 243 adefining boss hole 243 b. The lower portion of camshaft 206 in boss hole243 b is formed with a hemispheric detent recess 202 open at an outerperipheral surface thereof. Detent recess 202 defines either unbrakingrotational angle P4 a or braking rotational angle P4 b. In this regard,when rotated cam shaft 206 reaches either unbraking rotational angle P4a or braking rotational angle P4 b, detent recess 202 coincides to hole243 d. Two detent recesses 202 may be formed in camshaft 206 so as todefine respective unbraking and braking rotational angles P4 a and P4 bof camshaft 206.

The open end of hole 243 d at the outer side surface of clutch unitcasing 242 is plugged by a cap 217, which may be a bolt screwed intoclutch unit casing 242. A detent ball 218 is disposed at the open end ofhole 243 d facing the outer peripheral surface of camshaft 206. Acompressed spring 219 is disposed in hole 243 d so as to be interposedbetween cap 217 and detent ball 218 so as to press detent ball 218against the outer peripheral surface of camshaft 206. Therefore, as soonas detent recess 202 comes to coincide to hole 243 d, detent ball 218 isthrust into detent recess 202, thereby retaining camshaft 206 atcorresponding unbraking or braking rotational angle P4 a or P4 b.

Each of upper and lower cam plates 211 is formed as an orthodox pearshaped cam having a circular base portion 204 peripherally surroundingcamshaft 206, and a triangular lobe portion 204 projecting horizontallyfrom base portion 205. Upper and lower cam plates 211 are identical toeach other in shape, and are arranged so as to completely overlap eachother when viewed in the vertical axial direction of camshaft 206. Dueto the rearward biasing force of wave washer 214, rear end surface 213 cof brake shift sleeve 213 is constantly pressed against upper and lowercam plates 211 regardless of the rotational angle of camshaft 206.

When cam 210 is disposed at unbraking rotational angle P4 a, circularportions 205 of upper and lower cam plates 211 abut against rear endsurface 213 c of brake shift sleeve 213. This position of brake shiftsleeve 213 where rear end surface 213 c abuts against circular baseportions 205 of upper and lower cam plates 211 is defined as anunbraking position P3 a of brake shift sleeve 213, which is the rearmostslide position of brake shift sleeve 213 along clutch input shaft 237,so that pawls 213 a of brake shift sleeve 213 are disposed rearward awayfrom pawls 212 b of brake flange 212, whereby brake shift sleeve 213disengages from brake flange 212, i.e., cam input shaft 237spline-fitted to brake shift sleeve 213 is allowed to rotate freely frombrake flange 212 fixed to clutch unit casing 242.

When cam 210 is disposed at braking rotational angle P4 b, ends 204 a oflobe portions 204 of upper and lower cam plates 211 abut against rearend surface 213 c of brake shift sleeve 213. This position of brakeshift sleeve 213 where rear end surface 213 c abuts against ends 204 aof lobe portions 204 of upper and lower cam plates 211 is defined as abraking position P3 b of brake shift sleeve 213, which is the foremostslide position of brake shift sleeve 213 along clutch input shaft 237,so that pawls 213 a of brake shift sleeve 213 mesh with pawls 212 b ofbrake flange 212, whereby brake shift sleeve 213 engages with brakeflange 212, i.e., cam input shaft 237 spline-fitted to brake shiftsleeve 213 is braked by brake flange 212 fixed to clutch unit casing242.

While pawls 213 a mesh with pawls 212 b, brake flange 212 applies acounterforce Tf3 onto brake shift sleeve 213. This counterforce Tf3functions as a rearward thrusting force Tf4 to push brake shift sleeve213 rearward in unbraking direction Ds. When viewed in plan (or bottomas shown in FIG. 27), the point on rear end surface 213 c of brake shiftsleeve 213 abutting against end 204 a of lobe portion 204 of each camplate 211 is aligned with axis C4 of camshaft 206 on a fore-and-aftforce activation line Lt coinciding to a lube centerline of lube portion204 of pear shaped cam plate 211. Rearward thrusting force Tf4 isactivated along this line Lt. Therefore, ends 204 a of lobe portions 204of cam plates 211 receive rearward thrusting force Tf4 plump withoutdiverting. In other words, rearward thrusting force Tf4 does not act torotate cam plates 211 rightward or leftward, but acts to resist therotation of camshaft 206 centered on axis C4, thereby stably retainingcam 210 at braking position 273.

Referring to FIGS. 28 and 29, an alternative clutch unit 339 is similarto clutch units 139 and 239 except that clutch unit 339 is configured soas to incorporate an alternative parking brake 341. Clutch unit 339includes a clutch unit casing 342. Clutch unit casing 342 includes amain housing 343, and an upper housing 344 joined to an upper portion ofmain housing 343. Main housing 343 journals input shaft 338, i.e., aclutch input shaft 337 and an unshown clutch output shaft joinedcoaxially to each other similar to clutch input and output shafts 138 aand 138 b. Main housing 343 is formed therein with a front clutchchamber 342 a and a rear brake chamber 342 b, similar to clutch chamber232 a and brake chamber 232 b in clutch unit casing 242.

Parking brake 341 includes a lock pin 328 and a brake flange 329, and isprovided with a cam mechanism including a cam 311 for operating lock pin328. Brake flange 329 is an approximately discoidal member having anouter peripheral surface. Brake flange 329 is formed with right and leftrectangular engagement projections 349 radially centrifugally rightwardand leftward from the outer peripheral surface of brake flange 329.

In this regard, main housing 343 is formed to have a laterally middlebottom arcuate portion, which is disposed along a lower portion of theouter peripheral surface of brake flange 329. Main housing 343 is formedat right and left portions thereof with respective rectangular bendingportions 343 a defining right and left recesses 350. Right engagementprojection 349 is fitted into right recess 350 so that its front, rear,bottom and right end surfaces are disposed along front, rear, bottom andright walls of right rectangular bending portion 343 a of main housing343. Left engagement projection 349 is fitted into left recess 350 sothat its front, rear, bottom and left end surfaces are disposed alongfront, rear, left and bottom walls of left rectangular bending portion343 a of main housing 343.

Further, upper housing 344 is formed with right and left support walls344 a extended downward in brake chamber 342 a. Each of right and leftsupport walls 344 a has an arcuate shaped surface that is disposed alongeach of right and left upper portions of the outer peripheral edge ofbrake flange 329. Further, each of right and left support walls 344 ahas a horizontal surface that is disposed along each of upper surfacesof right and left engagement projections 349 so as to define an upperend of each of right and left recesses 350.

Therefore, brake flange 329 is retained at its outer peripheral surfaceby main housing 343 and upper housing 344, and is held at right and leftengagement projections 349 in right and left recesses 350 defined byhousings 343 and 344 so as to be hindered from moving in the peripheraldirection and in the axial direction with respect to the fore-and-aftaxis of clutch input shaft 337. In this way, brake flange 329 is fixedto clutch unit casing 342. Brake flange 329 has a center hole throughwhich clutch input shaft 337 is passed so that clutch input shaft 337 isallowed to rotate relative to brake flange 329.

The portion of clutch input shaft 337 surrounded by the inner peripheralsurface of brake flange 329 defining the center hole of brake flange 329is formed with a plurality of (in this embodiment, four) hemisphericdetent recesses 336, which are open at an outer peripheral surface ofclutch input shaft 337 and are aligned in the peripheral direction ofclutch input shaft 337. A laterally middle upper portion of brake flange329 is formed as a boss portion 359 bored by a vertical guide hole 369.Guide hole 369 has an upper end open at a top portion of the outerperipheral surface of brake flange 329, and has a bottom end open at atop portion of the inner peripheral surface of brake flange 329. Avertical lock pin 328 is vertically slidably fitted in guide hole 369. Abottom portion of lock pin 328 is hemispheric shaped in correspondenceto the hemispheric shape of each detent recess 336.

An upper portion of lock pin 328 projects upward from the top end ofguide hole 369. A spring retaining plate 331 is vertically slidablyfitted on the upper portion of lock pin 328, and retaining ring 333 isfixed on the upper portion of lock pin 328 so as to prevent springretaining plate 331 from sliding further upward from the limit positiondefined by retaining ring 333. Right and left upper portions of brakeflange 329 are squarely cut off, so as to form right and left endvertical surfaces of boss portion 359, and so as to form right and leftshoulder surfaces 379 extended horizontally rightward and leftward fromlower ends of the right and left end vertical surfaces of boss portion359. A spring 332 is coiled around boss portion 359 of brake flange 329between spring retainer plate 331 and right and left shoulder surfaces379. Right and left support walls 344 a of upper housing 344 are formedto define a spring chamber 351 that is extended upward from brakechamber 342 b so as to incorporate the upper portion of lock pin 328,spring retaining plate 331, spring 332 and retaining ring 333.

An upper portion of upper housing 344 is formed to define a cam chamber352 extended upward from spring chamber 351 so as to incorporate a camplate 312 of cam 311. A laterally horizontal shaft hole 353 is formed inupper housing 344 so as to pass through cam chamber 352. A horizontalcamshaft 313 is fitted in shaft hole 353 so as to be rotatable centeredon its horizontal axis C5, and is fixedly provided thereon with camplate 312 in cam chamber 352. An end of camshaft 313 projects outwardfrom a right or left (in this embodiment, left) end surface of upperhousing 344, i.e., clutch unit casing 342, so as to be operativelyconnected to parking brake lever 189 via link 188. A retaining plate 335is fastened onto the top end surface of upper housing 244 by a bolt orthe like (not shown), and is partly fitted into annular groove 317 so asto prevent camshaft 313 from laterally escaping from upper housing 344.

Cam plate 312 is formed as an orthodox pear shaped cam having a circularbase portion 314 peripherally surrounding camshaft 313, and a triangularlobe portion 315 projecting horizontally from base portion 314. Ahemispheric head 348 of lock pin 328 is pressed against cam plate 312above lock pin 328 by a biasing force of spring 332.

When cam 311 is disposed at unbraking rotational angle P6 a, lobeportion 315 of cam plate 312 is extended horizontally so that circularbase portion 314 of cam plate 312 abuts against head 348 of lock pin328. This position of head 348 of lock pin 328 is defined as anunbraking position P5 a of lock pin 328, which is the uppermost slideposition of lock pin 328 along guide hole 369, so that the bottomportion of lock pin 328 is disposed upward away from the outerperipheral surface of clutch input shaft 337, thereby allowing clutchinput shaft 337 to rotate free from lock pin 328.

When cam 311 is rotated to braking rotational angle P6 b, cam plate 312is rotated to extend lobe portion 315 downward. Due to the downwardextension of lobe portion 315 of cam plate 312, spring 332 is compressedso as to press the bottom portion of lock pin 328 against the outerperipheral surface of clutch input shaft 337. Therefore, as soon asclutch input shaft 337 is located in its rotational direction so thatthe bottom end of guide hole 369 coincides to one of detent recesses336, the bottom portion of lock pin 328 is fitted into detent recess336, thereby braking clutch input shaft 337. The position of head 348 oflock pin 328, where the bottom of lock pin 328 is fitted in detentrecess 336, is defined as a braking position P5 b of lock pin 328, whichis the lowermost slide position of lock pin 328 along guide hole 369.Therefore, cam 311 completely reaches braking rotational angle P6 b.

While lock pin 328 is disposed at braking position P5 b, lobe portion315 of cam plate 312 is extended exactly vertically downward, so that atip end of lobe portion 315 abuts against a top end 334 of head 348 oflock pin 328, whereby cam plate 312 abutting against lock pin 328 isbalanced so as not to tend to rotate from braking position P6 b. In thisstate, clutch input shaft 337 applies a counterforce Tf5 onto a bottomend of lock pin 328. This counterforce Tf5 functions as an upwardthrusting force Tf6 to push lock pin 328 upward in an unbrakingdirection Dt. Top end 334 of head 348 of lock pin 328 and the bottom endof lock pin 328 are aligned on a vertical force activation line Lucoinciding to a lube centerline of lube portion 315 of pear shaped camplate 312. Upward thrusting force Tf6 is activated along this line Lu.Therefore, the end of lobe portion 315 of cam plate 312 receives upwardthrusting force Tf6 plump without diverting. In other words, upwardthrusting force Tf6 does not act to rotate cam plate 312 rightward orleftward, but acts to resist the rotation of camshaft 313 centered onaxis C5, thereby stably retaining cam 311 at braking position P6 b.

It is further understood by those skilled in the art that the foregoingdescription is a preferred embodiment of the disclosed device and thatvarious changes and modifications may be made in the invention withoutdeparting from the scope thereof defined by the following claims.

1-9. (canceled)
 10. A brake mechanism for braking a target rotarymember, the brake mechanism comprising: a lock member shiftable betweena lock position, where the lock member engages with the target rotarymember to brake the target rotary member, and an unlock position, wherethe lock member disengages from the target rotary member to unbrake thetarget rotary member; and a cam member rotatable centered on an axis soas to be shiftable between a brake operation position to locate the lockmember at the lock position and an unbrake operation position to locatethe lock member at the unlock position, wherein, when the cam member isdisposed at the brake operation position, the lock member and the cammember contact each other at a contact point on a radial line extendingfrom the axis of the cam member, and wherein a direction of the radialline coincides to a direction of a counterforce of the target rotarymember against the lock member engaging with the target rotary member,so that a rotational force of the cam member is not applied to the lockmember at the contact point.
 11. The brake mechanism according to claim10, wherein the lock member is rotatable between the lock position andthe unlock position, wherein the cam member has a cam hole surrounded byan edge surface of the cam member; wherein the lock member has a contactportion disposed in the cam hole to contact the edge surface of the cammember, wherein the cam hole is bent to have a braking area and anunbraking area, wherein, when the cam member is disposed at the unbrakeoperation position, the contact portion of the lock member is disposedin the unbraking area of the cam hole so as to locate the lock member atthe lock position, and wherein, when the cam member is disposed at thebrake operation position, the contact portion of the lock membercontacts the edge surface of the cam member in the braking area of thecam hole at the contact point so as to hold the lock member at theunlock position.
 12. The brake mechanism according to claim 10, whereinthe lock member is slidable along an axis of the target rotary memberbetween the lock position and the unlock position, wherein the cammember has a protrusion extended in a radial direction from the axis ofthe cam member, wherein, when the cam member is disposed at the brakeoperation position, the protrusion of the cam member contacts a surfaceof the lock member at the contact point so as to hold the lock member atthe lock position, and wherein, when the cam member is disposed at theunbrake operation position, the protrusion of the cam member does notcontact the lock member so that the lock member is located at the unlockposition.
 13. The brake mechanism according to claim 10, wherein thelock member is slidable in a radial direction of the target rotarymember between the lock position and the unlock position, wherein thecam member has a protrusion extended in a radial direction from the axisof the cam member, wherein, when the cam member is disposed at the brakeoperation position, the protrusion of the cam member contacts a surfaceof the lock member at the contact point so as to hold the lock member atthe lock position, and wherein, when the cam member is disposed at theunbrake operation position, the protrusion of the cam member does notcontact the lock member so that the lock member is located at the unlockposition.